Planck 2013 results. XX. Cosmology from Sunyaev-Zeldovich cluster counts. (arXiv:1303.5080v1 [astro-ph.CO]):
We present constraints on cosmological parameters using number counts as a
function of redshift for a sub-sample of 189 galaxy clusters from the Planck SZ
(PSZ) catalogue. The PSZ is selected through the signature of the
Sunyaev--Zeldovich (SZ) effect, and the sub-sample used here has a
signal-to-noise threshold of seven, with each object confirmed as a cluster and
all but one with a redshift estimate. We discuss the calculation of the
expected cluster counts as a function of cosmological parameters, the
completeness of the sample, and the likelihood construction method. Using a
relation between mass M and SZ signal Y based on comparison to X-ray
measurements, we derive constraints on the power spectrum amplitude sigma_8 and
matter density parameter \Omega_m in a flat LCDM model. We test the robustness
of our estimates and find that possible biases in the Y-M relation and the halo
mass function appear larger than the statistical uncertainties from the cluster
sample. Assuming a bias between the X-ray determined mass and the true mass of
20%, motivated by comparison of the observed mass scaling relations to those
from a set of numerical simulations, we find that
sigma_8(Omega_m/0.27)^0.3=0.78+-0.01, with one-dimensional ranges
sigma_8=0.77+-0.02 and Omega_m=0.29+-0.02. The values of the cosmological
parameters are degenerate with the mass bias, and it is found that the larger
values of sigma_8 and Omega_m preferred by the Planck's measurements of the
primary CMB anisotropies can be accommodated by a mass bias of about 45%.
Alternatively, consistency with the primary CMB constraints can be achieved by
inclusion of processes that suppress power on small scales, such as a component
of massive neutrinos. We place our results in the context of other
determinations of cosmological parameters, and discuss issues that need to be
resolved in order to make progress in this field.
Monday, March 25, 2013
Sunday, March 24, 2013
Planck 2013 results. XXIX. Planck catalogue of Sunyaev-Zeldovich sources. (arXiv:1303.5089v1 [astro-ph.CO])
Planck 2013 results. XXIX. Planck catalogue of Sunyaev-Zeldovich sources. (arXiv:1303.5089v1 [astro-ph.CO]):
We describe the all-sky Planck catalogue of clusters and cluster candidates
derived from Sunyaev--Zeldovich (SZ) effect detections using the first 15.5
months of Planck satellite observations. The catalogue contains 1227 entries,
making it over six times the size of the Planck Early SZ (ESZ) sample and the
largest SZ-selected catalogue to date. It contains 861 confirmed clusters, of
which 178 have been confirmed as clusters, mostly through follow-up
observations, and a further 683 are previously-known clusters. The remaining
366 have the status of cluster candidates, and we divide them into three
classes according to the quality of evidence that they are likely to be true
clusters. The Planck SZ catalogue is the deepest all-sky cluster catalogue,
with redshifts up to about one, and spans the broadest cluster mass range from
(0.1 to 1.6) 10^{15}Msun. Confirmation of cluster candidates through comparison
with existing surveys or cluster catalogues is extensively described, as is the
statistical characterization of the catalogue in terms of completeness and
statistical reliability. The outputs of the validation process are provided as
additional information. This gives, in particular, an ensemble of 813 cluster
redshifts, and for all these Planck clusters we also include a mass estimated
from a newly-proposed SZ-mass proxy. A refined measure of the SZ Compton
parameter for the clusters with X-ray counter-parts is provided, as is an X-ray
flux for all the Planck clusters not previously detected in X-ray surveys.
We describe the all-sky Planck catalogue of clusters and cluster candidates
derived from Sunyaev--Zeldovich (SZ) effect detections using the first 15.5
months of Planck satellite observations. The catalogue contains 1227 entries,
making it over six times the size of the Planck Early SZ (ESZ) sample and the
largest SZ-selected catalogue to date. It contains 861 confirmed clusters, of
which 178 have been confirmed as clusters, mostly through follow-up
observations, and a further 683 are previously-known clusters. The remaining
366 have the status of cluster candidates, and we divide them into three
classes according to the quality of evidence that they are likely to be true
clusters. The Planck SZ catalogue is the deepest all-sky cluster catalogue,
with redshifts up to about one, and spans the broadest cluster mass range from
(0.1 to 1.6) 10^{15}Msun. Confirmation of cluster candidates through comparison
with existing surveys or cluster catalogues is extensively described, as is the
statistical characterization of the catalogue in terms of completeness and
statistical reliability. The outputs of the validation process are provided as
additional information. This gives, in particular, an ensemble of 813 cluster
redshifts, and for all these Planck clusters we also include a mass estimated
from a newly-proposed SZ-mass proxy. A refined measure of the SZ Compton
parameter for the clusters with X-ray counter-parts is provided, as is an X-ray
flux for all the Planck clusters not previously detected in X-ray surveys.
Mass And Radius Constraints Using Magnetar Giant Flare Oscillations. (arXiv:1303.3270v1 [astro-ph.HE])
Mass And Radius Constraints Using Magnetar Giant Flare Oscillations. (arXiv:1303.3270v1 [astro-ph.HE]):
We study crustal oscillations in magnetars including corrections for a finite
Alfv\'en velocity. Our crust model uses a new nuclear mass formula that
predicts nuclear masses with an accuracy very close to that of the Finite Range
Droplet Model. This mass model for equilibrium nuclei also includes recent
developments in the nuclear physics, in particular, shell corrections and an
updated neutron-drip line. We perturb our crust model to predict axial crust
modes and assign them to observed giant flare quasi-periodic oscillation (QPO)
frequencies from SGR 1806-20. The QPOs associated with the fundamental and
first harmonic can be used to constrain magnetar masses and radii. We use these
modes and the phenomenological equations of state from Steiner et al. to find a
magnetar crust which reproduces observations of SGR 1806-20. We find magnetar
crusts that match observations for various magnetic field strengths,
entrainment of the free neutron gas in the inner crust, and crust-core
transition densities. Matching observations with a field-free model we obtain
the approximate values of M =1.35 Msun and R = 11.9 km. Matching observations
using a model with the surface dipole field of SGR 1806-20 (B=2.4x10^15 G) we
obtain the approximate values of M = 1.25 Msun and R = 12.4 km. Without
significant entrainment of the free neutron gas the magnetar requires a larger
mass and radius to reproduce observations. If the crust-core transition occurs
at a lower density the magnetar requires a lower mass and a larger radius to
reproduce observations.
We study crustal oscillations in magnetars including corrections for a finite
Alfv\'en velocity. Our crust model uses a new nuclear mass formula that
predicts nuclear masses with an accuracy very close to that of the Finite Range
Droplet Model. This mass model for equilibrium nuclei also includes recent
developments in the nuclear physics, in particular, shell corrections and an
updated neutron-drip line. We perturb our crust model to predict axial crust
modes and assign them to observed giant flare quasi-periodic oscillation (QPO)
frequencies from SGR 1806-20. The QPOs associated with the fundamental and
first harmonic can be used to constrain magnetar masses and radii. We use these
modes and the phenomenological equations of state from Steiner et al. to find a
magnetar crust which reproduces observations of SGR 1806-20. We find magnetar
crusts that match observations for various magnetic field strengths,
entrainment of the free neutron gas in the inner crust, and crust-core
transition densities. Matching observations with a field-free model we obtain
the approximate values of M =1.35 Msun and R = 11.9 km. Matching observations
using a model with the surface dipole field of SGR 1806-20 (B=2.4x10^15 G) we
obtain the approximate values of M = 1.25 Msun and R = 12.4 km. Without
significant entrainment of the free neutron gas the magnetar requires a larger
mass and radius to reproduce observations. If the crust-core transition occurs
at a lower density the magnetar requires a lower mass and a larger radius to
reproduce observations.
The hottest superfluid and superconductor in the Universe: Discovery and nuclear physics implications. (arXiv:1303.3282v2 [hep-ph] UPDATED)
The hottest superfluid and superconductor in the Universe: Discovery and nuclear physics implications. (arXiv:1303.3282v2 [hep-ph] UPDATED):
We present recent work on using astronomical observations of neutron stars to
reveal unique insights into nuclear matter that cannot be obtained from
laboratories on Earth. First, we discuss our measurement of the rapid cooling
of the youngest neutron star in the Galaxy; this provides the first direct
evidence for superfluidity and superconductivity in the supra-nuclear core of
neutron stars. We show that observations of thermonuclear X-ray bursts on
neutron stars can be used to constrain properties of neutron superfluidity and
neutrino emission. We describe the implications of rapid neutron star rotation
rates on aspects of nuclear and superfluid physics. Finally, we show that
entrainment coupling between the neutron superfluid and the nuclear lattice
leads to a less mobile crust superfluid; this result puts into question the
conventional picture of pulsar glitches as being solely due to the crust
superfluid and suggests that the core superfluid also participates.
We present recent work on using astronomical observations of neutron stars to
reveal unique insights into nuclear matter that cannot be obtained from
laboratories on Earth. First, we discuss our measurement of the rapid cooling
of the youngest neutron star in the Galaxy; this provides the first direct
evidence for superfluidity and superconductivity in the supra-nuclear core of
neutron stars. We show that observations of thermonuclear X-ray bursts on
neutron stars can be used to constrain properties of neutron superfluidity and
neutrino emission. We describe the implications of rapid neutron star rotation
rates on aspects of nuclear and superfluid physics. Finally, we show that
entrainment coupling between the neutron superfluid and the nuclear lattice
leads to a less mobile crust superfluid; this result puts into question the
conventional picture of pulsar glitches as being solely due to the crust
superfluid and suggests that the core superfluid also participates.
Outskirts of Galaxy Clusters. (arXiv:1303.3286v1 [astro-ph.CO])
Outskirts of Galaxy Clusters. (arXiv:1303.3286v1 [astro-ph.CO]):
Until recently, only about 10% of the total intracluster gas volume had been
studied with high accuracy, leaving a vast region essentially unexplored. This
is now changing and a wide area of hot gas physics and chemistry awaits
discovery in galaxy cluster outskirts. Also, robust large-scale total mass
profiles and maps are within reach. First observational and theoretical results
in this emerging field have been achieved in recent years with sometimes
surprising findings. Here, we summarize and illustrate the relevant underlying
physical and chemical processes and review the recent progress in X-ray,
Sunyaev--Zel'dovich, and weak gravitational lensing observations of cluster
outskirts, including also brief discussions of technical challenges and
possible future improvements.
Until recently, only about 10% of the total intracluster gas volume had been
studied with high accuracy, leaving a vast region essentially unexplored. This
is now changing and a wide area of hot gas physics and chemistry awaits
discovery in galaxy cluster outskirts. Also, robust large-scale total mass
profiles and maps are within reach. First observational and theoretical results
in this emerging field have been achieved in recent years with sometimes
surprising findings. Here, we summarize and illustrate the relevant underlying
physical and chemical processes and review the recent progress in X-ray,
Sunyaev--Zel'dovich, and weak gravitational lensing observations of cluster
outskirts, including also brief discussions of technical challenges and
possible future improvements.
Mass profiles of Galaxy Clusters from X-ray analysis. (arXiv:1303.3530v1 [astro-ph.CO])
Mass profiles of Galaxy Clusters from X-ray analysis. (arXiv:1303.3530v1 [astro-ph.CO]):
We review the methods used at the present to reconstruct the mass profiles in
X-ray luminous galaxy clusters. We discuss the limitations and the biases
affecting these measurements and their cosmological implications.
We review the methods used at the present to reconstruct the mass profiles in
X-ray luminous galaxy clusters. We discuss the limitations and the biases
affecting these measurements and their cosmological implications.
Energy Extraction from Spinning Black Holes via Relativistic Jets. (arXiv:1303.3004v1 [astro-ph.HE])
Energy Extraction from Spinning Black Holes via Relativistic Jets. (arXiv:1303.3004v1 [astro-ph.HE]):
It has for long been an article of faith among astrophysicists that black
hole spin energy is responsible for powering the relativistic jets seen in
accreting black holes. Two recent advances have strengthened the case. First,
numerical general relativistic magnetohydrodynamic simulations of accreting
spinning black holes show that relativistic jets form spontaneously. In at
least some cases, there is unambiguous evidence that much of the jet energy
comes from the black hole, not the disk. Second, spin parameters of a number of
accreting stellar-mass black holes have been measured. For ballistic jets from
these systems, it is found that the radio luminosity of the jet correlates with
the spin of the black hole. This suggests a causal relationship between black
hole spin and jet power, presumably due to a generalized Penrose process.
It has for long been an article of faith among astrophysicists that black
hole spin energy is responsible for powering the relativistic jets seen in
accreting black holes. Two recent advances have strengthened the case. First,
numerical general relativistic magnetohydrodynamic simulations of accreting
spinning black holes show that relativistic jets form spontaneously. In at
least some cases, there is unambiguous evidence that much of the jet energy
comes from the black hole, not the disk. Second, spin parameters of a number of
accreting stellar-mass black holes have been measured. For ballistic jets from
these systems, it is found that the radio luminosity of the jet correlates with
the spin of the black hole. This suggests a causal relationship between black
hole spin and jet power, presumably due to a generalized Penrose process.
Quasars Probing Quasars IV: Joint Constraints on the Circumgalactic Medium from Absorption and Emission. (arXiv:1303.2708v1 [astro-ph.CO])
Quasars Probing Quasars IV: Joint Constraints on the Circumgalactic Medium from Absorption and Emission. (arXiv:1303.2708v1 [astro-ph.CO]):
We have constructed a sample of 29 close projected quasar pairs where the
background quasar spectrum reveals absorption from optically thick HI gas
associated with the foreground quasar. These unique sightlines allow us to
study the quasar circumgalactic medium (CGM) in absorption and emission
simultaneously, because the background quasar pinpoints large concentrations of
gas where Ly-a emission, resulting from quasar-powered fluorescence, resonant
Ly-a scattering, and/or cooling radiation, is expected. A sensitive
slit-spectroscopic search (1-sigma limits of SB_Lya ~= 3e-18
erg/s/cm^2/arcsec^2) for diffuse Ly-a emission in the environments of the
foreground quasars is conducted. We fail to detect large-scale ~ 100 kpc Ly-a
emission, either at the location of the optically thick absorbers or in the
foreground quasar halos, in all cases except a single system. We interpret
these non-detections as evidence that the gas detected in absorption is
shadowed from the quasar UV radiation due to obscuration effects, which are
frequently invoked in unified models of AGN. Small-scale R_perp <~ 50 kpc
extended Ly-a nebulosities are detected in 34% of our sample, which are likely
the high-redshift analogs of the extended emission-line regions commonly
observed around low-redshift (z < 0.5) quasars. We also detect a compact high
rest-frame equivalent width (W_Lya > 50 A) Ly-alpha-emitter with luminosity
L_Lya =2.1+-0.32e41 erg/s at small impact parameter R_perp=134 kpc from one
foreground quasar, and argue that it is more likely to result from
quasar-powered fluorescence, than simply be a star-forming galaxy clustered
around the quasar. Our observations imply that much deeper integrations with
upcoming integral-field spectrometers such as MUSE and KCWI will be able to
routinely detect a diffuse Ly-a glow around bright quasars on scales R ~ 100
kpc and thus directly image the CGM. [abridged]
We have constructed a sample of 29 close projected quasar pairs where the
background quasar spectrum reveals absorption from optically thick HI gas
associated with the foreground quasar. These unique sightlines allow us to
study the quasar circumgalactic medium (CGM) in absorption and emission
simultaneously, because the background quasar pinpoints large concentrations of
gas where Ly-a emission, resulting from quasar-powered fluorescence, resonant
Ly-a scattering, and/or cooling radiation, is expected. A sensitive
slit-spectroscopic search (1-sigma limits of SB_Lya ~= 3e-18
erg/s/cm^2/arcsec^2) for diffuse Ly-a emission in the environments of the
foreground quasars is conducted. We fail to detect large-scale ~ 100 kpc Ly-a
emission, either at the location of the optically thick absorbers or in the
foreground quasar halos, in all cases except a single system. We interpret
these non-detections as evidence that the gas detected in absorption is
shadowed from the quasar UV radiation due to obscuration effects, which are
frequently invoked in unified models of AGN. Small-scale R_perp <~ 50 kpc
extended Ly-a nebulosities are detected in 34% of our sample, which are likely
the high-redshift analogs of the extended emission-line regions commonly
observed around low-redshift (z < 0.5) quasars. We also detect a compact high
rest-frame equivalent width (W_Lya > 50 A) Ly-alpha-emitter with luminosity
L_Lya =2.1+-0.32e41 erg/s at small impact parameter R_perp=134 kpc from one
foreground quasar, and argue that it is more likely to result from
quasar-powered fluorescence, than simply be a star-forming galaxy clustered
around the quasar. Our observations imply that much deeper integrations with
upcoming integral-field spectrometers such as MUSE and KCWI will be able to
routinely detect a diffuse Ly-a glow around bright quasars on scales R ~ 100
kpc and thus directly image the CGM. [abridged]
The Halo Occupation Distribution of X-ray-Bright Active Galactic Nuclei: A Comparison with Luminous Quasars. (arXiv:1303.2942v1 [astro-ph.CO])
The Halo Occupation Distribution of X-ray-Bright Active Galactic Nuclei: A Comparison with Luminous Quasars. (arXiv:1303.2942v1 [astro-ph.CO]):
We perform halo occupation distribution (HOD) modeling of the projected
two-point correlation function (2PCF) of high-redshift (z~1.2) X-ray-bright
active galactic nuclei (AGN) in the XMM-COSMOS field measured by Allevato et
al. The HOD parameterization is based on low-luminosity AGN in cosmological
simulations. At the median redshift of z~1.2, we derive a median mass of
(1.02+0.21/-0.23)x10^{13} Msun/h for halos hosting central AGN and an upper
limit of ~10% on the AGN satellite fraction. Our modeling results indicate (at
the 2.5-sigma level) that X-ray AGN reside in more massive halos compared to
more bolometrically luminous, optically-selected quasars at similar redshift.
The modeling also yields constraints on the duty cycle of the X-ray AGN, and we
find that at z~1.2 the average duration of the X-ray AGN phase is two orders of
magnitude longer than that of the quasar phase. Our inferred mean occupation
function of X-ray AGN is similar to recent empirical measurements with a group
catalog and suggests that AGN halo occupancy increases with increasing halo
mass. We project the XMM-COSMOS 2PCF measurements to forecast the required
survey parameters needed in future AGN clustering studies to enable higher
precision HOD constraints and determinations of key physical parameters like
the satellite fraction and duty cycle. We find that N^{2}/A~5x10^{6} deg^{-2}
(with N the number of AGN in a survey area of A deg^{2}) is sufficient to
constrain the HOD parameters at the 10% level, which is easily achievable by
upcoming and proposed X-ray surveys.
We perform halo occupation distribution (HOD) modeling of the projected
two-point correlation function (2PCF) of high-redshift (z~1.2) X-ray-bright
active galactic nuclei (AGN) in the XMM-COSMOS field measured by Allevato et
al. The HOD parameterization is based on low-luminosity AGN in cosmological
simulations. At the median redshift of z~1.2, we derive a median mass of
(1.02+0.21/-0.23)x10^{13} Msun/h for halos hosting central AGN and an upper
limit of ~10% on the AGN satellite fraction. Our modeling results indicate (at
the 2.5-sigma level) that X-ray AGN reside in more massive halos compared to
more bolometrically luminous, optically-selected quasars at similar redshift.
The modeling also yields constraints on the duty cycle of the X-ray AGN, and we
find that at z~1.2 the average duration of the X-ray AGN phase is two orders of
magnitude longer than that of the quasar phase. Our inferred mean occupation
function of X-ray AGN is similar to recent empirical measurements with a group
catalog and suggests that AGN halo occupancy increases with increasing halo
mass. We project the XMM-COSMOS 2PCF measurements to forecast the required
survey parameters needed in future AGN clustering studies to enable higher
precision HOD constraints and determinations of key physical parameters like
the satellite fraction and duty cycle. We find that N^{2}/A~5x10^{6} deg^{-2}
(with N the number of AGN in a survey area of A deg^{2}) is sufficient to
constrain the HOD parameters at the 10% level, which is easily achievable by
upcoming and proposed X-ray surveys.
Optical counterparts of the nearest ultraluminous X-ray sources. (arXiv:1303.1213v1 [astro-ph.HE])
Optical counterparts of the nearest ultraluminous X-ray sources. (arXiv:1303.1213v1 [astro-ph.HE]):
We present a photometric survey of the optical counterparts of ultraluminous
X-ray sources (ULXs) observed with the Hubble Space Telescope in nearby (< 5
Mpc) galaxies. Of the 33 ULXs with Hubble & Chandra data, 9 have no visible
counterpart, placing limits on their M_V of ~ -4 to -9, enabling us to rule out
O-type companions in 4 cases. The refined positions of two ULXs place them in
the nucleus of their host galaxy. They are removed from our sample. Of the 22
remaining ULXs, 13 have one possible optical counterpart, while multiple are
visible within the error regions of other ULXs. By calculating the number of
chance coincidences, we estimate that 13 +/- 5 are the true counterparts. We
attempt to constrain the nature of the companions by fitting the SED and M_V to
obtain candidate spectral types. We can rule out O-type companions in 20 cases,
while we find that one ULX (NGC 253 ULX2) excludes all OB-type companions.
Fitting with X-ray irradiated models provides constraints on the donor star
mass and radius. For 7 ULXs, we are able to impose inclination-dependent upper
and/or lower limits on the black holes mass, if the extinction to the assumed
companion star is not larger than the Galactic column. These are NGC 55 ULX1,
NGC 253 ULX1, NGC 253 ULX2, NGC 253 XMM6, Ho IX X-1, IC342 X-1 & NGC 5204 X-1.
This suggests that 10 ULXs do not have O companions, while none of the 18
fitted rule out B-type companions.
We present a photometric survey of the optical counterparts of ultraluminous
X-ray sources (ULXs) observed with the Hubble Space Telescope in nearby (< 5
Mpc) galaxies. Of the 33 ULXs with Hubble & Chandra data, 9 have no visible
counterpart, placing limits on their M_V of ~ -4 to -9, enabling us to rule out
O-type companions in 4 cases. The refined positions of two ULXs place them in
the nucleus of their host galaxy. They are removed from our sample. Of the 22
remaining ULXs, 13 have one possible optical counterpart, while multiple are
visible within the error regions of other ULXs. By calculating the number of
chance coincidences, we estimate that 13 +/- 5 are the true counterparts. We
attempt to constrain the nature of the companions by fitting the SED and M_V to
obtain candidate spectral types. We can rule out O-type companions in 20 cases,
while we find that one ULX (NGC 253 ULX2) excludes all OB-type companions.
Fitting with X-ray irradiated models provides constraints on the donor star
mass and radius. For 7 ULXs, we are able to impose inclination-dependent upper
and/or lower limits on the black holes mass, if the extinction to the assumed
companion star is not larger than the Galactic column. These are NGC 55 ULX1,
NGC 253 ULX1, NGC 253 ULX2, NGC 253 XMM6, Ho IX X-1, IC342 X-1 & NGC 5204 X-1.
This suggests that 10 ULXs do not have O companions, while none of the 18
fitted rule out B-type companions.
Evolution of accreting white dwarfs; some of them continue to grow. (arXiv:1303.3642v1 [astro-ph.SR])
Evolution of accreting white dwarfs; some of them continue to grow. (arXiv:1303.3642v1 [astro-ph.SR]):
Novae are cataclysmic variable binary systems in which a white dwarf primary
is accreting material from a low mass companion. The importance of this
accretion takes on added significance if the WD can increase its mass to reach
the Chandrasekhar limit thus exploding as a Type Ia supernova. In this study we
accrete material of Solar composition onto carbon-oxygen white dwarfs of 0.70,
1.00 and 1.35 Msun with accretion rates from 1.6e-10 to 1.6e-6 Msun per yr. We
have utilized the MESA stellar evolution code for our modeling and evolve them
for many nova cycles or, in some cases, evolution to a red giant stage.
Differing behaviors occur as a function of both the WD mass and the accretion
rate. For the lower WD masses, the models undergo recurrent hydrogen flashes at
low accretion rates; for higher accretion rates, steady-burning of hydrogen
occurs and eventually gives way to recurrent hydrogen flashes. At the highest
accretion rates, these models go through a steady-burning phase but eventually
transition into red giants. For the highest white dwarf mass recurrent hydrogen
flashes occur at lower accretion rates but for higher rates the models exhibit
steady-burning interspersed with helium flashes. We find that for all our
models that undergo recurrent hydrogen flashes, as well as the steady-burning
models that exhibit helium flashes, the mass of the WD continues to grow toward
the Chandrasekhar limit. These results suggest that the accretion of Solar
abundance material onto carbon-oxygen white dwarfs in cataclysmic variable
systems, the single degenerate scenario, is a viable channel for progenitors of
Type Ia supernova explosions.
Novae are cataclysmic variable binary systems in which a white dwarf primary
is accreting material from a low mass companion. The importance of this
accretion takes on added significance if the WD can increase its mass to reach
the Chandrasekhar limit thus exploding as a Type Ia supernova. In this study we
accrete material of Solar composition onto carbon-oxygen white dwarfs of 0.70,
1.00 and 1.35 Msun with accretion rates from 1.6e-10 to 1.6e-6 Msun per yr. We
have utilized the MESA stellar evolution code for our modeling and evolve them
for many nova cycles or, in some cases, evolution to a red giant stage.
Differing behaviors occur as a function of both the WD mass and the accretion
rate. For the lower WD masses, the models undergo recurrent hydrogen flashes at
low accretion rates; for higher accretion rates, steady-burning of hydrogen
occurs and eventually gives way to recurrent hydrogen flashes. At the highest
accretion rates, these models go through a steady-burning phase but eventually
transition into red giants. For the highest white dwarf mass recurrent hydrogen
flashes occur at lower accretion rates but for higher rates the models exhibit
steady-burning interspersed with helium flashes. We find that for all our
models that undergo recurrent hydrogen flashes, as well as the steady-burning
models that exhibit helium flashes, the mass of the WD continues to grow toward
the Chandrasekhar limit. These results suggest that the accretion of Solar
abundance material onto carbon-oxygen white dwarfs in cataclysmic variable
systems, the single degenerate scenario, is a viable channel for progenitors of
Type Ia supernova explosions.
An X-rays Survey of the Young Stellar Population of the Lynds 1641 and Iota Orionis Regions. (arXiv:1303.3996v1 [astro-ph.SR])
An X-rays Survey of the Young Stellar Population of the Lynds 1641 and Iota Orionis Regions. (arXiv:1303.3996v1 [astro-ph.SR]):
We present an XMM-Newton survey of the part of Orion A cloud south of the
Orion Nebula. This survey includes the Lynds 1641 (L1641) dark cloud, a region
of the Orion A cloud with very few massive stars and hence a relatively low
ambient UV flux, and the region around the O9 III star Iota Orionis. In
addition to proprietary data, we used archival XMM data of the Orion Nebula
Cluster (ONC) to extend our analysis to a major fraction of the Orion A cloud.
We have detected 1060 X-ray sources in L1641 and Iota Ori region. About 94% of
the sources have 2MASS & Spitzer counterparts, 204 and 23 being Class II and
Class I or protostars objects, respectively. In addition, we have identified
489 X-ray sources as counterparts to Class III candidates, given they are
bright in X-rays and appear as normal photospheres at mid-IR wavelengths. The
remaining 205 X-ray sources are likely distant AGNs or other galactic sources
not related to Orion A. We find that Class III candidates appear more
concentrated in two main clusters in L1641. The first cluster of Class III
stars is found toward the northern part of L1641, concentrated around Iota Ori.
The stars in this cluster are more evolved than those in the Orion Nebula. We
estimate a distance of 300-320 pc for this cluster and thus it is closer than
the Orion A cloud. Another cluster rich in Class III stars is located in L1641
South and appears to be a slightly older cluster embedded in the Orion A cloud.
Furthermore, other evolved Class III stars are found north of the ONC toward
NGC 1977.
We present an XMM-Newton survey of the part of Orion A cloud south of the
Orion Nebula. This survey includes the Lynds 1641 (L1641) dark cloud, a region
of the Orion A cloud with very few massive stars and hence a relatively low
ambient UV flux, and the region around the O9 III star Iota Orionis. In
addition to proprietary data, we used archival XMM data of the Orion Nebula
Cluster (ONC) to extend our analysis to a major fraction of the Orion A cloud.
We have detected 1060 X-ray sources in L1641 and Iota Ori region. About 94% of
the sources have 2MASS & Spitzer counterparts, 204 and 23 being Class II and
Class I or protostars objects, respectively. In addition, we have identified
489 X-ray sources as counterparts to Class III candidates, given they are
bright in X-rays and appear as normal photospheres at mid-IR wavelengths. The
remaining 205 X-ray sources are likely distant AGNs or other galactic sources
not related to Orion A. We find that Class III candidates appear more
concentrated in two main clusters in L1641. The first cluster of Class III
stars is found toward the northern part of L1641, concentrated around Iota Ori.
The stars in this cluster are more evolved than those in the Orion Nebula. We
estimate a distance of 300-320 pc for this cluster and thus it is closer than
the Orion A cloud. Another cluster rich in Class III stars is located in L1641
South and appears to be a slightly older cluster embedded in the Orion A cloud.
Furthermore, other evolved Class III stars are found north of the ONC toward
NGC 1977.
Collisional and Radiative Processes in Optically Thin Plasmas. (arXiv:1303.4468v1 [astro-ph.SR])
Collisional and Radiative Processes in Optically Thin Plasmas. (arXiv:1303.4468v1 [astro-ph.SR]):
Most of our knowledge of the physical processes in distant plasmas is
obtained through measurement of the radiation they produce. Here we provide an
overview of the main collisional and radiative processes and examples of
diagnostics relevant to the microphysical processes in the plasma. Many
analyses assume a time-steady plasma with ion populations in equilibrium with
the local temperature and Maxwellian distributions of particle velocities, but
these assumptions are easily violated in many cases. We consider these
departures from equilibrium and possible diagnostics in detail.
Most of our knowledge of the physical processes in distant plasmas is
obtained through measurement of the radiation they produce. Here we provide an
overview of the main collisional and radiative processes and examples of
diagnostics relevant to the microphysical processes in the plasma. Many
analyses assume a time-steady plasma with ion populations in equilibrium with
the local temperature and Maxwellian distributions of particle velocities, but
these assumptions are easily violated in many cases. We consider these
departures from equilibrium and possible diagnostics in detail.
Rapid cooling of Cas A as a phase transition in dense QCD. (arXiv:1303.5380v1 [astro-ph.HE])
Rapid cooling of Cas A as a phase transition in dense QCD. (arXiv:1303.5380v1 [astro-ph.HE]):
We present a model of the compact star in Cassiopea A, which accommodates its
unusually fast cooling behavior. This feature is interpreted as due to an
enhancement in the neutrino emission triggered by a transition from fully
gapped two-flavor color superconducting phase to a crystalline or an
alternative gapless color superconducting phase. By fine-tuning a single
parameter -- the temperature of this transition - a specific cooling scenario
can be selected that fits the Cas A data. Such scenario requires as a
prerequisite a massive M ~ 2M_{sun}$ star and is, therefore, distinctive from
models invoking canonical 1.4 M_{sun} mass star with nucleonic pairing only.
We present a model of the compact star in Cassiopea A, which accommodates its
unusually fast cooling behavior. This feature is interpreted as due to an
enhancement in the neutrino emission triggered by a transition from fully
gapped two-flavor color superconducting phase to a crystalline or an
alternative gapless color superconducting phase. By fine-tuning a single
parameter -- the temperature of this transition - a specific cooling scenario
can be selected that fits the Cas A data. Such scenario requires as a
prerequisite a massive M ~ 2M_{sun}$ star and is, therefore, distinctive from
models invoking canonical 1.4 M_{sun} mass star with nucleonic pairing only.
Planck 2013 results X. Energetic particle effects: characterization, removal, and simulation. (arXiv:1303.5071v1 [astro-ph.CO])
Planck 2013 results X. Energetic particle effects: characterization, removal, and simulation. (arXiv:1303.5071v1 [astro-ph.CO]):
This paper presents the detection, interpretation and removal of the signal
resulting from interactions of high energy particles with the Planck High
Frequency Instrument (HFI). These interactions fall into two categories,
heating the 0.1 K bolometer plate and glitches in each detector time stream.
Glitch shapes are not simple single pole exponential decays and fall into a
three families. The glitch shape for each family has been characterized
empirically in flight data and removed from the detector time streams. The
spectrum of the count rate/unit energy is computed for each family and a
correspondence to where on the detector the particle hit is made. Most of the
detected glitches are from galactic protons incident on the Si die frame
supporting the micromachined bolometric detectors. At HFI, the particle flux is
~ 5 per square cm and per second and is dominated by protons incident on the
spacecraft with an energy >39 MeV, leading to a rate of typically one event per
second and per detector. Different categories of glitches have different
signature in timestreams. Two of the glitch types have a low amplitude
component that decays over nearly 1 second. This component produces an excess
noise if not properly removed from the time ordered data. We have used a glitch
detection and subtraction method based on the joint fit of population
templates. The application of this novel glitch removal method removes excess
noise from glitches. Using realistic simulations, we find this method does not
introduce signal bias.
RKS Note: Planck is in the same orbit as all proposed future X-ray missions, so this background will likely be the same.
This paper presents the detection, interpretation and removal of the signal
resulting from interactions of high energy particles with the Planck High
Frequency Instrument (HFI). These interactions fall into two categories,
heating the 0.1 K bolometer plate and glitches in each detector time stream.
Glitch shapes are not simple single pole exponential decays and fall into a
three families. The glitch shape for each family has been characterized
empirically in flight data and removed from the detector time streams. The
spectrum of the count rate/unit energy is computed for each family and a
correspondence to where on the detector the particle hit is made. Most of the
detected glitches are from galactic protons incident on the Si die frame
supporting the micromachined bolometric detectors. At HFI, the particle flux is
~ 5 per square cm and per second and is dominated by protons incident on the
spacecraft with an energy >39 MeV, leading to a rate of typically one event per
second and per detector. Different categories of glitches have different
signature in timestreams. Two of the glitch types have a low amplitude
component that decays over nearly 1 second. This component produces an excess
noise if not properly removed from the time ordered data. We have used a glitch
detection and subtraction method based on the joint fit of population
templates. The application of this novel glitch removal method removes excess
noise from glitches. Using realistic simulations, we find this method does not
introduce signal bias.
RKS Note: Planck is in the same orbit as all proposed future X-ray missions, so this background will likely be the same.
Equation of state and neutron star properties constrained by nuclear physics and observation. (arXiv:1303.4662v1 [astro-ph.SR])
Equation of state and neutron star properties constrained by nuclear physics and observation. (arXiv:1303.4662v1 [astro-ph.SR]):
Microscopic calculations of neutron matter based on nuclear interactions
derived from chiral effective field theory, combined with the recent
observation of a 1.97 +- 0.04 M_sun neutron star, constrain the equation of
state of neutron-rich matter at sub- and supranuclear densities. We discuss in
detail the allowed equations of state and the impact of our results on the
structure of neutron stars, the crust-core transition density, and the nuclear
symmetry energy. In particular, we show that the predicted range for neutron
star radii is robust. For use in astrophysical simulations, we provide detailed
numerical tables for a representative set of equations of state consistent with
these constraints.
Microscopic calculations of neutron matter based on nuclear interactions
derived from chiral effective field theory, combined with the recent
observation of a 1.97 +- 0.04 M_sun neutron star, constrain the equation of
state of neutron-rich matter at sub- and supranuclear densities. We discuss in
detail the allowed equations of state and the impact of our results on the
structure of neutron stars, the crust-core transition density, and the nuclear
symmetry energy. In particular, we show that the predicted range for neutron
star radii is robust. For use in astrophysical simulations, we provide detailed
numerical tables for a representative set of equations of state consistent with
these constraints.
Planck 2013 results. I. Overview of products and scientific results. (arXiv:1303.5062v1 [astro-ph.CO])
Planck 2013 results. I. Overview of products and scientific results. (arXiv:1303.5062v1 [astro-ph.CO]):
The ESA's Planck satellite, dedicated to studying the early universe, was
launched on May 2009 and has been surveying the microwave and submillimetre sky
since August 2009. In March 2013, ESA and the Planck Collaboration publicly
released the initial cosmology products based on the first 15.5 months of
Planck operations, along with a set of scientific and technical papers and a
web-based explanatory supplement. This paper describes the mission and its
performance, and gives an overview of the processing and analysis of the data,
the characteristics of the data, the main scientific results, and the science
data products and papers in the release. Scientific results include robust
support for the standard, six parameter LCDM model of cosmology and improved
measurements for the parameters that define this model, including a highly
significant deviation from scale invariance of the primordial power spectrum.
The Planck values for some of these parameters and others derived from them are
significantly different from those previously determined. Several large scale
anomalies in the CMB temperature distribution detected earlier by WMAP are
confirmed with higher confidence. Planck sets new limits on the number and mass
of neutrinos, and has measured gravitational lensing of CMB anisotropies at 25
sigma. Planck finds no evidence for non-Gaussian statistics of the CMB
anisotropies. There is some tension between Planck and WMAP results; this is
evident in the power spectrum and results for some of the cosmology parameters.
In general, Planck results agree well with results from the measurements of
baryon acoustic oscillations. Because the analysis of Planck polarization data
is not yet as mature as the analysis of temperature data, polarization results
are not released. We do, however, illustrate the robust detection of the E-mode
polarization signal around CMB hot- and cold-spots.
The ESA's Planck satellite, dedicated to studying the early universe, was
launched on May 2009 and has been surveying the microwave and submillimetre sky
since August 2009. In March 2013, ESA and the Planck Collaboration publicly
released the initial cosmology products based on the first 15.5 months of
Planck operations, along with a set of scientific and technical papers and a
web-based explanatory supplement. This paper describes the mission and its
performance, and gives an overview of the processing and analysis of the data,
the characteristics of the data, the main scientific results, and the science
data products and papers in the release. Scientific results include robust
support for the standard, six parameter LCDM model of cosmology and improved
measurements for the parameters that define this model, including a highly
significant deviation from scale invariance of the primordial power spectrum.
The Planck values for some of these parameters and others derived from them are
significantly different from those previously determined. Several large scale
anomalies in the CMB temperature distribution detected earlier by WMAP are
confirmed with higher confidence. Planck sets new limits on the number and mass
of neutrinos, and has measured gravitational lensing of CMB anisotropies at 25
sigma. Planck finds no evidence for non-Gaussian statistics of the CMB
anisotropies. There is some tension between Planck and WMAP results; this is
evident in the power spectrum and results for some of the cosmology parameters.
In general, Planck results agree well with results from the measurements of
baryon acoustic oscillations. Because the analysis of Planck polarization data
is not yet as mature as the analysis of temperature data, polarization results
are not released. We do, however, illustrate the robust detection of the E-mode
polarization signal around CMB hot- and cold-spots.
Tuesday, March 12, 2013
X-ray reflected spectra from accretion disk models. III. A complete grid of ionized reflection calculations. (arXiv:1303.2112v1 [astro-ph.HE])
X-ray reflected spectra from accretion disk models. III. A complete grid of ionized reflection calculations. (arXiv:1303.2112v1 [astro-ph.HE]):
We present a new and complete library of synthetic spectra for modeling the
component of emission that is reflected from an illuminated accretion disk. The
spectra were computed using an updated version of our code XILLVER that
incorporates new routines and a richer atomic data base. We offer in the form
of a table model an extensive grid of reflection models that cover a wide range
of parameters. Each individual model is characterized by the photon index
\Gamma of the illuminating radiation, the ionization parameter \xi at the
surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and
the iron abundance A_{Fe} relative to the solar value. The ranges of the
parameters covered are: 1.2 \leq \Gamma \leq 3.4, 1 \leq \xi \leq 10^4, and 0.5
\leq A_{Fe} \leq 10. These ranges capture the physical conditions typically
inferred from observations of active galactic nuclei, and also stellar-mass
black holes in the hard state. This library is intended for use when the
thermal disk flux is faint compared to the incident power-law flux. The models
are expected to provide an accurate description of the Fe K emission line,
which is the crucial spectral feature used to measure black hole spin. A total
of 720 reflection spectra are provided in a single FITS
file{\url{this http URL}} suitable for the
analysis of X-ray observations via the atable model in XSPEC. Detailed
comparisons with previous reflection models illustrate the improvements
incorporated in this version of XILLVER.
We present a new and complete library of synthetic spectra for modeling the
component of emission that is reflected from an illuminated accretion disk. The
spectra were computed using an updated version of our code XILLVER that
incorporates new routines and a richer atomic data base. We offer in the form
of a table model an extensive grid of reflection models that cover a wide range
of parameters. Each individual model is characterized by the photon index
\Gamma of the illuminating radiation, the ionization parameter \xi at the
surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and
the iron abundance A_{Fe} relative to the solar value. The ranges of the
parameters covered are: 1.2 \leq \Gamma \leq 3.4, 1 \leq \xi \leq 10^4, and 0.5
\leq A_{Fe} \leq 10. These ranges capture the physical conditions typically
inferred from observations of active galactic nuclei, and also stellar-mass
black holes in the hard state. This library is intended for use when the
thermal disk flux is faint compared to the incident power-law flux. The models
are expected to provide an accurate description of the Fe K emission line,
which is the crucial spectral feature used to measure black hole spin. A total
of 720 reflection spectra are provided in a single FITS
file{\url{this http URL}} suitable for the
analysis of X-ray observations via the atable model in XSPEC. Detailed
comparisons with previous reflection models illustrate the improvements
incorporated in this version of XILLVER.
The S2 star as a probe of the accretion disk of Sgr A*. (arXiv:1303.2115v1 [astro-ph.HE])
The S2 star as a probe of the accretion disk of Sgr A*. (arXiv:1303.2115v1 [astro-ph.HE]):
How accretion proceeds around the massive black hole in the Galactic center
and other highly sub-Eddington accretors remains poorly understood. The orbit
of the S2 star in the Galactic center passes through the accretion disk of the
massive black hole and any observational signature from such interaction may be
used as an accretion probe. Because of its early stellar type, S2 is expected
to possess a fairly powerful wind. We show here that the ram pressure of the
accretion disk shocks the stellar wind fairly close to the star. The shocked
fluid reaches a temperature of ~ 1 keV and cools efficiently through optically
thin, thermal bremsstrahlung emission. The radiation from the shocked wind
peaks around the epoch of the pericenter passage of the star at a luminosity
potentially comparable to the quiescent emission detected from Sgr A*.
Detection of shocked wind radiation can constrain the density of the accretion
disk at a distance of several thousands of gravitational radii from the black
hole.
How accretion proceeds around the massive black hole in the Galactic center
and other highly sub-Eddington accretors remains poorly understood. The orbit
of the S2 star in the Galactic center passes through the accretion disk of the
massive black hole and any observational signature from such interaction may be
used as an accretion probe. Because of its early stellar type, S2 is expected
to possess a fairly powerful wind. We show here that the ram pressure of the
accretion disk shocks the stellar wind fairly close to the star. The shocked
fluid reaches a temperature of ~ 1 keV and cools efficiently through optically
thin, thermal bremsstrahlung emission. The radiation from the shocked wind
peaks around the epoch of the pericenter passage of the star at a luminosity
potentially comparable to the quiescent emission detected from Sgr A*.
Detection of shocked wind radiation can constrain the density of the accretion
disk at a distance of several thousands of gravitational radii from the black
hole.
The place of the Sun among the Sun-like stars. (arXiv:1303.2245v1 [astro-ph.SR])
The place of the Sun among the Sun-like stars. (arXiv:1303.2245v1 [astro-ph.SR]):
Context. Monitoring of the photometric and chromospheric HK emission data
series of stars similar to the Sun in age and average activity level showed
that there is an empirical correlation between the average stellar
chromospheric activity level and the photometric variability. In general, more
active stars show larger photometric variability. Interestingly, the
measurements and reconstructions of the solar irradiance show that the Sun is
significantly less variable than indicated by the empirical relationship. Aims.
We aim to identify possible reasons for the Sun to be currently outside of this
relationship. Methods. We employed different scenarios of solar HK emission and
irradiance variability and compared them with available time series of Sun-like
stars. Results. We show that the position of the Sun on the diagram of
photometric variability versus chromospheric activity changes with time. The
present solar position is different from its temporal mean position as the
satellite era of continuous solar irradiance measurements has accidentally
coincided with a period of unusually high and stable solar activity. Our
analysis suggests that although present solar variability is significantly
smaller than indicated by the stellar data, the temporal mean solar variability
might be in agreement with the stellar data. We propose that the continuation
of the photometric program and its expansion to a larger stellar sample will
ultimately allow us to constrain the historical solar variability.
Context. Monitoring of the photometric and chromospheric HK emission data
series of stars similar to the Sun in age and average activity level showed
that there is an empirical correlation between the average stellar
chromospheric activity level and the photometric variability. In general, more
active stars show larger photometric variability. Interestingly, the
measurements and reconstructions of the solar irradiance show that the Sun is
significantly less variable than indicated by the empirical relationship. Aims.
We aim to identify possible reasons for the Sun to be currently outside of this
relationship. Methods. We employed different scenarios of solar HK emission and
irradiance variability and compared them with available time series of Sun-like
stars. Results. We show that the position of the Sun on the diagram of
photometric variability versus chromospheric activity changes with time. The
present solar position is different from its temporal mean position as the
satellite era of continuous solar irradiance measurements has accidentally
coincided with a period of unusually high and stable solar activity. Our
analysis suggests that although present solar variability is significantly
smaller than indicated by the stellar data, the temporal mean solar variability
might be in agreement with the stellar data. We propose that the continuation
of the photometric program and its expansion to a larger stellar sample will
ultimately allow us to constrain the historical solar variability.
Individual Alpha Elements, C, N, and Ba in Early Type Galaxies. (arXiv:1303.2603v1 [astro-ph.CO])
Individual Alpha Elements, C, N, and Ba in Early Type Galaxies. (arXiv:1303.2603v1 [astro-ph.CO]):
Spectral data on early type galaxies is analyzed for chemical abundance with
an emphasis on obtaining detailed abundances for the elements O and Si in
addition to C, N, Na, Mg, Ca, Fe, and Ba. The abundance trends with velocity
dispersion fit preconceptions based upon previous Mg conclusions, namely that
larger galaxies have a higher alpha element to iron peak ratio indicative of a
higher ratio of Type II to Type Ia supernova products. The heaviest alpha
elements, Ca and Ti, do not participate in this trend, although this fact does
not necessarily alter the basic picture given the uncertainties in
nucleosynthetic yields. Elements that likely have significant contributions
from intermediate-mass stars, namely C, N, and Ba, also gain ground relative to
Fe in massive galaxies at a modest level, with the Ba conclusion uncertain from
our data alone.
Spectral data on early type galaxies is analyzed for chemical abundance with
an emphasis on obtaining detailed abundances for the elements O and Si in
addition to C, N, Na, Mg, Ca, Fe, and Ba. The abundance trends with velocity
dispersion fit preconceptions based upon previous Mg conclusions, namely that
larger galaxies have a higher alpha element to iron peak ratio indicative of a
higher ratio of Type II to Type Ia supernova products. The heaviest alpha
elements, Ca and Ti, do not participate in this trend, although this fact does
not necessarily alter the basic picture given the uncertainties in
nucleosynthetic yields. Elements that likely have significant contributions
from intermediate-mass stars, namely C, N, and Ba, also gain ground relative to
Fe in massive galaxies at a modest level, with the Ba conclusion uncertain from
our data alone.
Evidence for Two Distinct Populations of Type Ia Supernovae. (arXiv:1303.2601v1 [astro-ph.CO])
Evidence for Two Distinct Populations of Type Ia Supernovae. (arXiv:1303.2601v1 [astro-ph.CO]):
Type Ia supernovae (SNe Ia) have been used as excellent standardizable
candles for measuring cosmic expansion, but their progenitors are still
elusive. Here we report that the spectral diversity of SNe Ia is tied to their
birthplace environments. We find that those with high-velocity ejecta are
substantially more concentrated in the inner and brighter regions of their host
galaxies than are normal-velocity SNe Ia. Furthermore, the former tend to
inhabit larger and more-luminous hosts. These results suggest that
high-velocity SNe Ia likely originate from relatively younger and more
metal-rich progenitors than normal-velocity SNe Ia, and are restricted to
galaxies with substantial chemical evolution.
Type Ia supernovae (SNe Ia) have been used as excellent standardizable
candles for measuring cosmic expansion, but their progenitors are still
elusive. Here we report that the spectral diversity of SNe Ia is tied to their
birthplace environments. We find that those with high-velocity ejecta are
substantially more concentrated in the inner and brighter regions of their host
galaxies than are normal-velocity SNe Ia. Furthermore, the former tend to
inhabit larger and more-luminous hosts. These results suggest that
high-velocity SNe Ia likely originate from relatively younger and more
metal-rich progenitors than normal-velocity SNe Ia, and are restricted to
galaxies with substantial chemical evolution.
Thermal and dynamical properties of gas accreting onto a supermassive black hole in an AGN. (arXiv:1303.2341v1 [astro-ph.GA])
Thermal and dynamical properties of gas accreting onto a supermassive black hole in an AGN. (arXiv:1303.2341v1 [astro-ph.GA]):
(Abridged) We study stability of gas accretion in Active Galactic Nuclei. Our
grid based simulations cover a radial range from 0.1 to 200 pc. Here, as in
previous studies by our group, we include gas radiative cooling as well as
heating by a sub-Eddington X-ray source near the central supermassive black
hole of 10^8 M_{\odot}. Our theoretical estimates and simulations show that for
the X-ray luminosity L_X \sim 0.008 L_{Edd}, the gas is thermally and
convectivelly unstable within the computational domain. In the simulations, we
observe that very tiny fluctuations in an initially smooth, spherically
symmetric, accretion flow, grow first linearly and then non-linearly.
Consequently, an initially one-phase flow relatively quickly transitions into a
two-phase/cold-hot accretion flow. For L_X = 0.015 L_{Edd} or higher, the cold
clouds continue to accrete but in some regions of the hot phase, the gas starts
to move outward. For L_X < 0.015 L_{Edd}, the cold phase contribution to the
total mass accretion rate only moderately dominates over the hot phase
contribution. This result might have some consequences for cosmological
simulations of the so-called AGN feedback problem. Our simulations confirm the
previous results of Barai et al. (2012) who used smoothed particle hydrodynamic
simulations to tackle the same problem. However here, because we use a grid
based code to solve equations in 1-D and 2-D, we are able to follow the gas
dynamics at much higher spacial resolution and for longer time in comparison to
the 3-D SPH simulations. One of new features revealed by our simulations is
that the cold condensations in the accretion flow initially form long
filaments, but at the later times, those filaments may break into smaller
clouds advected outwards within the hot outflow. These simulations may serve as
an attractive model for the so-called Narrow Line Region in AGN.
(Abridged) We study stability of gas accretion in Active Galactic Nuclei. Our
grid based simulations cover a radial range from 0.1 to 200 pc. Here, as in
previous studies by our group, we include gas radiative cooling as well as
heating by a sub-Eddington X-ray source near the central supermassive black
hole of 10^8 M_{\odot}. Our theoretical estimates and simulations show that for
the X-ray luminosity L_X \sim 0.008 L_{Edd}, the gas is thermally and
convectivelly unstable within the computational domain. In the simulations, we
observe that very tiny fluctuations in an initially smooth, spherically
symmetric, accretion flow, grow first linearly and then non-linearly.
Consequently, an initially one-phase flow relatively quickly transitions into a
two-phase/cold-hot accretion flow. For L_X = 0.015 L_{Edd} or higher, the cold
clouds continue to accrete but in some regions of the hot phase, the gas starts
to move outward. For L_X < 0.015 L_{Edd}, the cold phase contribution to the
total mass accretion rate only moderately dominates over the hot phase
contribution. This result might have some consequences for cosmological
simulations of the so-called AGN feedback problem. Our simulations confirm the
previous results of Barai et al. (2012) who used smoothed particle hydrodynamic
simulations to tackle the same problem. However here, because we use a grid
based code to solve equations in 1-D and 2-D, we are able to follow the gas
dynamics at much higher spacial resolution and for longer time in comparison to
the 3-D SPH simulations. One of new features revealed by our simulations is
that the cold condensations in the accretion flow initially form long
filaments, but at the later times, those filaments may break into smaller
clouds advected outwards within the hot outflow. These simulations may serve as
an attractive model for the so-called Narrow Line Region in AGN.
Photoionization modeling of oxygen K absorption in the interstellar medium:the Chandra grating spectra of XTE J1817-330. (arXiv:1303.2396v1 [astro-ph.HE])
Photoionization modeling of oxygen K absorption in the interstellar medium:the Chandra grating spectra of XTE J1817-330. (arXiv:1303.2396v1 [astro-ph.HE]):
We present detailed analyses of oxygen K absorption in the interstellar
medium (ISM) using four high-resolution Chandra spectra towards the X-ray
low-mass binary XTE J1817-330. The 11-25 A broadband is described with a simple
absorption model that takes into account the pileup effect and results in an
estimate of the hydrogen column density. The oxygen K-edge region (21-25 A) is
fitted with the physical warmabs model, which is based on a photoionization
model grid generated with the xstar code with the most up-to-date atomic
database. This approach allows a benchmark of the atomic data which involves
wavelength shifts of both the K lines and photoionization cross sections in
order to fit the observed spectra accurately. As a result we obtain: a column
density of N(H)=1.38+/-0.01\times 10^21 cm^-2; ionization parameter of
log(xi)=-2.70+/-0.023; oxygen abundance of A(O)= 0.689^{+0.015}_{-0.010}; and
ionization fractions of OI/O = 0.911, OII/O = 0.077, and OIII/O = 0.012 that
are in good agreement with previous studies. Since the oxygen abundance in
warmabs is given relative to the solar standard of Grevesse et al. (1998), a
rescaling with the revision by Asplund et al. (2009) yields
A(O)=0.952^{+0.020}_{-0.013}, a value close to solar that reinforces the new
standard. We identify several atomic absorption lines Kalpha, Kbeta, and Kgamma
in OI and OII; and Kalpha in OIII, OVI, and OVII - last two probably residing
in the neighborhood of the source rather than in the ISM. This is the first
firm detection of oxygen K resonances with principal quantum numbers n>2
associated to ISM cold absorption.
We present detailed analyses of oxygen K absorption in the interstellar
medium (ISM) using four high-resolution Chandra spectra towards the X-ray
low-mass binary XTE J1817-330. The 11-25 A broadband is described with a simple
absorption model that takes into account the pileup effect and results in an
estimate of the hydrogen column density. The oxygen K-edge region (21-25 A) is
fitted with the physical warmabs model, which is based on a photoionization
model grid generated with the xstar code with the most up-to-date atomic
database. This approach allows a benchmark of the atomic data which involves
wavelength shifts of both the K lines and photoionization cross sections in
order to fit the observed spectra accurately. As a result we obtain: a column
density of N(H)=1.38+/-0.01\times 10^21 cm^-2; ionization parameter of
log(xi)=-2.70+/-0.023; oxygen abundance of A(O)= 0.689^{+0.015}_{-0.010}; and
ionization fractions of OI/O = 0.911, OII/O = 0.077, and OIII/O = 0.012 that
are in good agreement with previous studies. Since the oxygen abundance in
warmabs is given relative to the solar standard of Grevesse et al. (1998), a
rescaling with the revision by Asplund et al. (2009) yields
A(O)=0.952^{+0.020}_{-0.013}, a value close to solar that reinforces the new
standard. We identify several atomic absorption lines Kalpha, Kbeta, and Kgamma
in OI and OII; and Kalpha in OIII, OVI, and OVII - last two probably residing
in the neighborhood of the source rather than in the ISM. This is the first
firm detection of oxygen K resonances with principal quantum numbers n>2
associated to ISM cold absorption.
Monday, March 11, 2013
The X-ray Properties of Optically Selected Clusters of Galaxies. (arXiv:1303.1819v1 [astro-ph.CO])
The X-ray Properties of Optically Selected Clusters of Galaxies. (arXiv:1303.1819v1 [astro-ph.CO]):
We present the results of Chandra and Suzaku X-ray observations of nine
moderate-redshift (0.16 < z < 0.42) clusters discovered via the Red-sequence
Cluster Survey (RCS). Surface brightness profiles are fitted to beta models,
gas masses are determined, integrated spectra are extracted within R2500, and
X-ray temperatures and luminosities are inferred. The Lx-Tx relationship
expected from self-similar evolution is tested by comparing this sample to our
previous X-ray investigation of nine high-redshift (0.6 < z < 1.0) optically
selected clusters. We find that optically selected clusters are systematically
less luminous than X-ray selected clusters of similar X-ray temperature at both
moderate and high-z. We are unable to constrain evolution in the Lx-Tx relation
with these data, but find it consistent with no evolution, within relatively
large uncertainties. To investigate selection effects, we compare the X-ray
properties of our sample to those of clusters in the representative X-ray
selected REXCESS sample, also determined within R2500. We find that while RCS
cluster X-ray properties span the entire range of those of massive clusters
selected by other methods, their average X-ray properties are most similar to
those of dynamically disturbed X-ray selected clusters. This similarity
suggests that the true cluster distribution might contain a higher fraction of
disturbed objects than are typically detected in X-ray selected surveys.
We present the results of Chandra and Suzaku X-ray observations of nine
moderate-redshift (0.16 < z < 0.42) clusters discovered via the Red-sequence
Cluster Survey (RCS). Surface brightness profiles are fitted to beta models,
gas masses are determined, integrated spectra are extracted within R2500, and
X-ray temperatures and luminosities are inferred. The Lx-Tx relationship
expected from self-similar evolution is tested by comparing this sample to our
previous X-ray investigation of nine high-redshift (0.6 < z < 1.0) optically
selected clusters. We find that optically selected clusters are systematically
less luminous than X-ray selected clusters of similar X-ray temperature at both
moderate and high-z. We are unable to constrain evolution in the Lx-Tx relation
with these data, but find it consistent with no evolution, within relatively
large uncertainties. To investigate selection effects, we compare the X-ray
properties of our sample to those of clusters in the representative X-ray
selected REXCESS sample, also determined within R2500. We find that while RCS
cluster X-ray properties span the entire range of those of massive clusters
selected by other methods, their average X-ray properties are most similar to
those of dynamically disturbed X-ray selected clusters. This similarity
suggests that the true cluster distribution might contain a higher fraction of
disturbed objects than are typically detected in X-ray selected surveys.
Strange star equation of state fits the refined mass measurement of 12 pulsars and predicts their radii. (arXiv:1303.1956v1 [astro-ph.HE])
Strange star equation of state fits the refined mass measurement of 12 pulsars and predicts their radii. (arXiv:1303.1956v1 [astro-ph.HE]):
There are three categories of stars whose masses have been found accurately
in recent times: (1) two for which Shapiro delay is used which is possible due
to GR light bending as the partner is heavy : PSR J1614-2230 and PSR J1903+0327
(2) six eclipsing stars for which numerical Roche Lobe geometry is used and (3)
3 stars for which spectroscopic methods are used and in fact for these three
the mass and radii both are estimated. Motivated by large color (N_c) expansion
using a modified Richardson potential, along with density dependent quark
masses thereby allowing chiral symmetry restoration, we get compact strange
stars fitting all the observed masses.
Sunday, March 10, 2013
X-ray absorption evolution in Gamma-Ray Bursts: intergalactic medium or evolutionary signature of their host galaxies?. (arXiv:1303.0844v1 [astro-ph.HE])
X-ray absorption evolution in Gamma-Ray Bursts: intergalactic medium or evolutionary signature of their host galaxies?. (arXiv:1303.0844v1 [astro-ph.HE]):
The intrinsic X-ray emission of Gamma-Ray Bursts (GRBs) is often found to be
absorbed over and above the column density through our own galaxy. The extra
component is usually assumed to be due to absorbing gas lying within the host
galaxy of the GRB itself. There is an apparent correlation between the
equivalent column density of hydrogen, N(H,intrinsic) (assuming it to be at the
GRB redshift), and redshift, z, with the few z>6 GRBs showing the greatest
intrinsic column densities. We investigate the N(H,intrinsic) - z relation
using a large sample of Swift GRBs, as well as active galactic nuclei (AGN) and
quasar samples, paying particular attention to the spectral energy
distributions of the two highest redshift GRBs. Various possible sample biases
and systematics that might produce such a correlation are considered, and we
conclude that the correlation is very likely to be real. This may indicate
either an evolutionary effect in the host galaxy properties, or a contribution
from gas along the line-of-sight, in the diffuse intergalactic medium (IGM) or
intervening absorbing clouds. Employing a more realistic model for IGM
absorption than in previous works, we find that this may explain much of the
observed opacity at z>~3 providing it is not too hot, likely between 10^5 K and
10^6.5 K, and moderately metal enriched, Z~0.2 Z_sun. This material could
therefore constitute the Warm Hot Intergalactic Medium. However, a comparable
level of absorption is also expected from the cumulative effect of intervening
cold gas clouds, and given current uncertainties it is not possible to say
which, if either, dominates. At lower redshifts, we conclude that gas in the
host galaxies must be the dominant contributor to the observed X-ray
absorption.
The intrinsic X-ray emission of Gamma-Ray Bursts (GRBs) is often found to be
absorbed over and above the column density through our own galaxy. The extra
component is usually assumed to be due to absorbing gas lying within the host
galaxy of the GRB itself. There is an apparent correlation between the
equivalent column density of hydrogen, N(H,intrinsic) (assuming it to be at the
GRB redshift), and redshift, z, with the few z>6 GRBs showing the greatest
intrinsic column densities. We investigate the N(H,intrinsic) - z relation
using a large sample of Swift GRBs, as well as active galactic nuclei (AGN) and
quasar samples, paying particular attention to the spectral energy
distributions of the two highest redshift GRBs. Various possible sample biases
and systematics that might produce such a correlation are considered, and we
conclude that the correlation is very likely to be real. This may indicate
either an evolutionary effect in the host galaxy properties, or a contribution
from gas along the line-of-sight, in the diffuse intergalactic medium (IGM) or
intervening absorbing clouds. Employing a more realistic model for IGM
absorption than in previous works, we find that this may explain much of the
observed opacity at z>~3 providing it is not too hot, likely between 10^5 K and
10^6.5 K, and moderately metal enriched, Z~0.2 Z_sun. This material could
therefore constitute the Warm Hot Intergalactic Medium. However, a comparable
level of absorption is also expected from the cumulative effect of intervening
cold gas clouds, and given current uncertainties it is not possible to say
which, if either, dominates. At lower redshifts, we conclude that gas in the
host galaxies must be the dominant contributor to the observed X-ray
absorption.
New Insights: the Accretion Process and Variable Wind from TW Hya. (arXiv:1303.1536v1 [astro-ph.SR])
New Insights: the Accretion Process and Variable Wind from TW Hya. (arXiv:1303.1536v1 [astro-ph.SR]):
For the first time in a classical T Tauri star, we are able to trace an
accretion event signaled by an hour-long enhancement of X-rays from the
accretion shock and revealed through substantial sequential changes in optical
emission line profiles. Downflowing turbulent material appears in H-alpha and
H-beta emission. He D3 (5876 Angstrom) broadens, coupled with an increase in
flux. Two hours after the X-ray accretion event, the optical veiling increases
due to continuum emission from the hot splashdown region. The response of the
stellar coronal emission to the heated photosphere follows about 2.4 hours
later, giving direct evidence that the stellar corona is heated in part by
accretion. Then, the stellar wind becomes re-established. A model that
incorporates the dynamics of this sequential series of events includes: an
accretion shock, a cooling downflow in a supersonically turbulent region,
followed by photospheric and later, coronal heating. This model naturally
explains the presence of broad optical and ultraviolet lines, and affects the
mass accretion rates currently determined from emission line profiles. These
results, coupled with the large heated coronal region revealed from X-ray
diagnostics, suggest that current models are not adequate to explain the
accretion process in young stars.
For the first time in a classical T Tauri star, we are able to trace an
accretion event signaled by an hour-long enhancement of X-rays from the
accretion shock and revealed through substantial sequential changes in optical
emission line profiles. Downflowing turbulent material appears in H-alpha and
H-beta emission. He D3 (5876 Angstrom) broadens, coupled with an increase in
flux. Two hours after the X-ray accretion event, the optical veiling increases
due to continuum emission from the hot splashdown region. The response of the
stellar coronal emission to the heated photosphere follows about 2.4 hours
later, giving direct evidence that the stellar corona is heated in part by
accretion. Then, the stellar wind becomes re-established. A model that
incorporates the dynamics of this sequential series of events includes: an
accretion shock, a cooling downflow in a supersonically turbulent region,
followed by photospheric and later, coronal heating. This model naturally
explains the presence of broad optical and ultraviolet lines, and affects the
mass accretion rates currently determined from emission line profiles. These
results, coupled with the large heated coronal region revealed from X-ray
diagnostics, suggest that current models are not adequate to explain the
accretion process in young stars.
The Impact of Starbursts on the Circumgalactic Medium. (arXiv:1303.1183v2 [astro-ph.CO] UPDATED)
The Impact of Starbursts on the Circumgalactic Medium. (arXiv:1303.1183v2 [astro-ph.CO] UPDATED):
We present a study exploring the impact of a starburst on the properties of
the surrounding circum-galactic medium (CGM): gas located beyond the galaxy's
stellar body and extending out to the virial radius (200 kpc). We obtained
ultraviolet spectroscopic data from the Cosmic Origin Spectrograph (COS)
probing the CGM of 20 low-redshift foreground galaxies using background QSOs.
Our sample consists of starburst and control galaxies. The latter comprises
normal star-forming and passive galaxies with similar stellar masses and impact
parameters as the starbursts. We used optical spectra from the Sloan Digital
Sky Survey(SDSS) to estimate the properties of the starbursts, inferring
average ages of 200 Myrs and burst fractions involving ~10% of their stellar
mass. The COS data reveal highly ionized gas traced by CIV in 80%(4/5) of the
starburst and in 17%(2/12) of the control sample. The two control galaxies with
CIV absorbers differed from the four starbursts in showing multiple
low-ionization transitions and strong saturated Lyman-alpha lines. They
therefore appear to be physically different systems. We show that the CIV
absorbers in the starburst CGM represent a significant baryon repository. The
high detection rate of this highly ionized material in the starbursts suggests
that starburst-driven winds can affect the CGM out to radii as large as 200
kpc. This is plausible given the inferred properties of the starbursts and the
known properties of starburst-driven winds. This would represent the first
direct observational evidence of local starbursts impacting the bulk of their
gaseous halos, and as such provides new evidence of the importance of this kind
of feedback in the evolution of galaxies.
We present a study exploring the impact of a starburst on the properties of
the surrounding circum-galactic medium (CGM): gas located beyond the galaxy's
stellar body and extending out to the virial radius (200 kpc). We obtained
ultraviolet spectroscopic data from the Cosmic Origin Spectrograph (COS)
probing the CGM of 20 low-redshift foreground galaxies using background QSOs.
Our sample consists of starburst and control galaxies. The latter comprises
normal star-forming and passive galaxies with similar stellar masses and impact
parameters as the starbursts. We used optical spectra from the Sloan Digital
Sky Survey(SDSS) to estimate the properties of the starbursts, inferring
average ages of 200 Myrs and burst fractions involving ~10% of their stellar
mass. The COS data reveal highly ionized gas traced by CIV in 80%(4/5) of the
starburst and in 17%(2/12) of the control sample. The two control galaxies with
CIV absorbers differed from the four starbursts in showing multiple
low-ionization transitions and strong saturated Lyman-alpha lines. They
therefore appear to be physically different systems. We show that the CIV
absorbers in the starburst CGM represent a significant baryon repository. The
high detection rate of this highly ionized material in the starbursts suggests
that starburst-driven winds can affect the CGM out to radii as large as 200
kpc. This is plausible given the inferred properties of the starbursts and the
known properties of starburst-driven winds. This would represent the first
direct observational evidence of local starbursts impacting the bulk of their
gaseous halos, and as such provides new evidence of the importance of this kind
of feedback in the evolution of galaxies.
Combining clustering and abundances of galaxy clusters to test cosmology and primordial non-Gaussianity. (arXiv:1303.0287v1 [astro-ph.CO])
Combining clustering and abundances of galaxy clusters to test cosmology and primordial non-Gaussianity. (arXiv:1303.0287v1 [astro-ph.CO]):
We present the clustering of galaxy clusters as a useful addition to the
common set of cosmological observables. The clustering of clusters probes the
large-scale structure of the Universe, extending galaxy clustering analysis to
the high-peak, high-bias regime. Clustering of galaxy clusters complements the
traditional cluster number counts and observable-mass relation analyses,
significantly improving their constraining power by breaking existing
calibration degeneracies. We use the maxBCG galaxy clusters catalogue to
constrain cosmological parameters and cross-calibrate the mass-observable
relation, using cluster abundances in richness bins and weak-lensing mass
estimates. We then add the redshift-space power spectrum of the sample,
including an effective modelling of the weakly non-linear contribution and
allowing for an arbitrary photometric redshift smoothing. The inclusion of the
power spectrum data allows for an improved self-calibration of the scaling
relation. We find that the inclusion of the power spectrum typically brings a
~50% improvement in the errors on the fluctuation amplitude sigma_8 and the
matter density Omega_m. Finally, we apply this method to constrain models of
the early universe through the amount of primordial non-Gaussianity of the
local type, using both the variation in the halo mass function and in the
cluster bias. We find a constraint on the amount of skewness f_NL = 12 +/- 157
(1 sigma) from the cluster data alone.
We present the clustering of galaxy clusters as a useful addition to the
common set of cosmological observables. The clustering of clusters probes the
large-scale structure of the Universe, extending galaxy clustering analysis to
the high-peak, high-bias regime. Clustering of galaxy clusters complements the
traditional cluster number counts and observable-mass relation analyses,
significantly improving their constraining power by breaking existing
calibration degeneracies. We use the maxBCG galaxy clusters catalogue to
constrain cosmological parameters and cross-calibrate the mass-observable
relation, using cluster abundances in richness bins and weak-lensing mass
estimates. We then add the redshift-space power spectrum of the sample,
including an effective modelling of the weakly non-linear contribution and
allowing for an arbitrary photometric redshift smoothing. The inclusion of the
power spectrum data allows for an improved self-calibration of the scaling
relation. We find that the inclusion of the power spectrum typically brings a
~50% improvement in the errors on the fluctuation amplitude sigma_8 and the
matter density Omega_m. Finally, we apply this method to constrain models of
the early universe through the amount of primordial non-Gaussianity of the
local type, using both the variation in the halo mass function and in the
cluster bias. We find a constraint on the amount of skewness f_NL = 12 +/- 157
(1 sigma) from the cluster data alone.
Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets. (arXiv:1303.1583v1 [astro-ph.HE])
Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets. (arXiv:1303.1583v1 [astro-ph.HE]):
The spins of ten stellar black holes have been measured using the
continuum-fitting method. These black holes are located in two distinct classes
of X-ray binary systems, one that is persistently X-ray bright and another that
is transient. Both the persistent and transient black holes remain for long
periods in a state where their spectra are dominated by a thermal accretion
disk component. The spin of a black hole of known mass and distance can be
measured by fitting this thermal continuum spectrum to the thin-disk model of
Novikov and Thorne; the key fit parameter is the radius of the inner edge of
the black hole's accretion disk. Strong observational and theoretical evidence
links the inner-disk radius to the radius of the innermost stable circular
orbit, which is trivially related to the dimensionless spin parameter a* (|a*|
\le 1). The ten spins that have so far been measured by this continuum-fitting
method range widely from a* \approx 0 to a* > 0.95. The robustness of the
method is demonstrated by the dozens or hundreds of independent and consistent
measurements of spin that have been obtained for several black holes, and
through careful consideration of many sources of systematic error. Among the
results discussed is a sharp dichotomy between the transient and persistent
black holes; the latter have higher spins and larger masses. Also discussed is
recently discovered evidence in the transient sources for a correlation between
the power of ballistic jets and black hole spin.
The spins of ten stellar black holes have been measured using the
continuum-fitting method. These black holes are located in two distinct classes
of X-ray binary systems, one that is persistently X-ray bright and another that
is transient. Both the persistent and transient black holes remain for long
periods in a state where their spectra are dominated by a thermal accretion
disk component. The spin of a black hole of known mass and distance can be
measured by fitting this thermal continuum spectrum to the thin-disk model of
Novikov and Thorne; the key fit parameter is the radius of the inner edge of
the black hole's accretion disk. Strong observational and theoretical evidence
links the inner-disk radius to the radius of the innermost stable circular
orbit, which is trivially related to the dimensionless spin parameter a* (|a*|
\le 1). The ten spins that have so far been measured by this continuum-fitting
method range widely from a* \approx 0 to a* > 0.95. The robustness of the
method is demonstrated by the dozens or hundreds of independent and consistent
measurements of spin that have been obtained for several black holes, and
through careful consideration of many sources of systematic error. Among the
results discussed is a sharp dichotomy between the transient and persistent
black holes; the latter have higher spins and larger masses. Also discussed is
recently discovered evidence in the transient sources for a correlation between
the power of ballistic jets and black hole spin.
Constraints on physics of neutron stars from X-ray observations. (arXiv:1303.0317v1 [astro-ph.HE])
Constraints on physics of neutron stars from X-ray observations. (arXiv:1303.0317v1 [astro-ph.HE]):
I summarize some constraints on the physics of neutron stars arising from
X-ray observations of the surfaces of neutron stars, focusing on using models
of low-magnetic-field neutron star atmospheres to interpret their X-ray
spectra. I discuss observations of spectral lines, pulsation profiles, X-ray
bursts, radius measurements of transiently accreting neutron stars in
quiescence, crust and core cooling measurements of transiently accreting
neutron stars, and cooling of young neutron stars. These observations have
constrained the neutron star mass and radius (and thus the internal
composition, and dense matter equation of state), the superfluidity and
neutrino emissivity properties of the core, and the composition and superfluid
state of the crust.
I summarize some constraints on the physics of neutron stars arising from
X-ray observations of the surfaces of neutron stars, focusing on using models
of low-magnetic-field neutron star atmospheres to interpret their X-ray
spectra. I discuss observations of spectral lines, pulsation profiles, X-ray
bursts, radius measurements of transiently accreting neutron stars in
quiescence, crust and core cooling measurements of transiently accreting
neutron stars, and cooling of young neutron stars. These observations have
constrained the neutron star mass and radius (and thus the internal
composition, and dense matter equation of state), the superfluidity and
neutrino emissivity properties of the core, and the composition and superfluid
state of the crust.
Star-planet interactions and selection effects from planet detection methods. (arXiv:1303.0307v1 [astro-ph.SR])
Star-planet interactions and selection effects from planet detection methods. (arXiv:1303.0307v1 [astro-ph.SR]):
Planets may have effects on their host stars by tidal or magnetic
interaction. Such star-planet interactions are thought to enhance the activity
level of the host star. However, stellar activity also affects the sensitivity
of planet detection methods. Samples of planet-hosting stars which are
investigated for such star-planet interactions are therefore subject to strong
selection effects which need to be taken into account.
RKS Note: Discusses X-ray implications
Planets may have effects on their host stars by tidal or magnetic
interaction. Such star-planet interactions are thought to enhance the activity
level of the host star. However, stellar activity also affects the sensitivity
of planet detection methods. Samples of planet-hosting stars which are
investigated for such star-planet interactions are therefore subject to strong
selection effects which need to be taken into account.
RKS Note: Discusses X-ray implications
AGN proximity zone fossils and the delayed recombination of metal lines. (arXiv:1303.0019v1 [astro-ph.CO])
AGN proximity zone fossils and the delayed recombination of metal lines. (arXiv:1303.0019v1 [astro-ph.CO]):
We model the time-dependent evolution of metal-enriched intergalactic and
circumgalactic gas exposed to the fluctuating radiation field from an active
galactic nucleus (AGN). We consider diffuse gas densities (n_H=10^-5-10^-3
cm^-3) exposed to the extra-galactic background (EGB) and initially in thermal
equilibrium (T \sim 10^4-10^4.5 K). Once the proximate AGN field turns on,
additional photo-ionisation rapidly ionises the HI and metals. The enhanced AGN
radiation field turns off after a typical AGN lifetime (tau_AGN=1-20 Myr) and
the field returns to the EGB intensity, but the metals remain out of ionisation
equilibrium for timescales that can significantly exceed tau_AGN. We define
this phase as the AGN proximity zone "fossil" phase and show that high
ionisation stages (e.g. OVI, NeVIII, MgX) are in general enhanced, while the
abundances of low ions are reduced. In contrast, HI re-equilibrates rapidly
(<<tau_AGN) owing to its low neutral fraction at diffuse densities. We
demonstrate that metal column densities of intervening gas observed in
absorption in quasar sight lines are significantly affected by delayed
recombination for a wide range of densities, metallicities, and AGN strengths,
lifetimes, and duty cycles. We model the exceptionally strong z=0.9 NeVIII
absorbers observed by Tripp et al. (2011) as arising in a possible fossil zone
or near a recently turned-on AGN and we demonstrate that at low redshift even
moderate strength AGN could significantly enhance the high-ion metal columns in
the circumgalactic media of galaxies observed without active AGN. Fossil
proximity zones may be particularly important during the quasar era, z \sim
2-5. AGN proximity zone fossils allow a whole new class of non-equilibrium
solutions that may be applicable to a large fraction of observed metal
absorbers and which could potentially change the inferred physical conditions
and masses of diffuse gases.
We model the time-dependent evolution of metal-enriched intergalactic and
circumgalactic gas exposed to the fluctuating radiation field from an active
galactic nucleus (AGN). We consider diffuse gas densities (n_H=10^-5-10^-3
cm^-3) exposed to the extra-galactic background (EGB) and initially in thermal
equilibrium (T \sim 10^4-10^4.5 K). Once the proximate AGN field turns on,
additional photo-ionisation rapidly ionises the HI and metals. The enhanced AGN
radiation field turns off after a typical AGN lifetime (tau_AGN=1-20 Myr) and
the field returns to the EGB intensity, but the metals remain out of ionisation
equilibrium for timescales that can significantly exceed tau_AGN. We define
this phase as the AGN proximity zone "fossil" phase and show that high
ionisation stages (e.g. OVI, NeVIII, MgX) are in general enhanced, while the
abundances of low ions are reduced. In contrast, HI re-equilibrates rapidly
(<<tau_AGN) owing to its low neutral fraction at diffuse densities. We
demonstrate that metal column densities of intervening gas observed in
absorption in quasar sight lines are significantly affected by delayed
recombination for a wide range of densities, metallicities, and AGN strengths,
lifetimes, and duty cycles. We model the exceptionally strong z=0.9 NeVIII
absorbers observed by Tripp et al. (2011) as arising in a possible fossil zone
or near a recently turned-on AGN and we demonstrate that at low redshift even
moderate strength AGN could significantly enhance the high-ion metal columns in
the circumgalactic media of galaxies observed without active AGN. Fossil
proximity zones may be particularly important during the quasar era, z \sim
2-5. AGN proximity zone fossils allow a whole new class of non-equilibrium
solutions that may be applicable to a large fraction of observed metal
absorbers and which could potentially change the inferred physical conditions
and masses of diffuse gases.
Testing the rotating hot spot model using X-ray burst oscillations from 4U 1636-536. (arXiv:1303.0248v1 [astro-ph.HE])
Testing the rotating hot spot model using X-ray burst oscillations from 4U 1636-536. (arXiv:1303.0248v1 [astro-ph.HE]):
Precise and accurate measurements of neutron star masses and radii would
provide valuable information about the still uncertain properties of cold
matter at supranuclear densities. One promising approach to making such
measurements involves analysis of the X-ray flux oscillations often seen during
thermonuclear (type 1) X-ray bursts. These oscillations are almost certainly
produced by emission from hotter regions on the stellar surface modulated by
the rotation of the star. One consequence of the rotation is that the
oscillation should appear earlier at higher photon energies than at lower
energies. Ford (1999) found compelling evidence for such a hard lead in the
tail oscillations of one type 1 burst from Aql X-1. We have therefore analyzed
individually the oscillations observed in the tails of the four type 1 bursts
from 4U 1636-536 that, when averaged, provided the strongest evidence for a
soft lead in the analysis by Muno et al. (2003). We have also analyzed the
oscillation observed during the superburst from this star. We find that the
data from these five bursts, treated both individually and jointly, are fully
consistent with a rotating hot spot model. Unfortunately, the uncertainties in
these data are too large to provide interesting constraints on the mass and
radius of this star.
Precise and accurate measurements of neutron star masses and radii would
provide valuable information about the still uncertain properties of cold
matter at supranuclear densities. One promising approach to making such
measurements involves analysis of the X-ray flux oscillations often seen during
thermonuclear (type 1) X-ray bursts. These oscillations are almost certainly
produced by emission from hotter regions on the stellar surface modulated by
the rotation of the star. One consequence of the rotation is that the
oscillation should appear earlier at higher photon energies than at lower
energies. Ford (1999) found compelling evidence for such a hard lead in the
tail oscillations of one type 1 burst from Aql X-1. We have therefore analyzed
individually the oscillations observed in the tails of the four type 1 bursts
from 4U 1636-536 that, when averaged, provided the strongest evidence for a
soft lead in the analysis by Muno et al. (2003). We have also analyzed the
oscillation observed during the superburst from this star. We find that the
data from these five bursts, treated both individually and jointly, are fully
consistent with a rotating hot spot model. Unfortunately, the uncertainties in
these data are too large to provide interesting constraints on the mass and
radius of this star.
HST/COS observations of a new population of associated QSO absorbers. (arXiv:1302.5510v1 [astro-ph.CO])
HST/COS observations of a new population of associated QSO absorbers. (arXiv:1302.5510v1 [astro-ph.CO]):
(Abridged) We present a sample of new population of associated absorbers,
detected through Ne VIII \lambda\lambda 770,780 absorption, in HST/COS spectra
of intermediate redshift (0.45 < z < 1.21) quasars (QSOs). Our sample comprised
of total 12 associated Ne VIII systems detected towards 8 lines of sight (none
of them are radio bright). The incidence rate of these absorbers is found to be
40%. Majority of the Ne VIII systems at small ejection velocities (v_ej) show
complete coverage of the background source, but systems with higher v_ej show
lower covering fractions (i.e. f_c < 0.8) and systematically higher values of
N(Ne VIII). We detect Mg X \lambda\lambda 609,624 absorption in 7 out of the 8
Ne VIII systems where the expected wavelength range is cover by our spectra and
is free of any strong blending. We report the detections of Na IX
\lambda\lambda 681,694 absorption, for the first time, in three highest
ejection velocity (e.g. v_ej > 7,000 km/s) systems in our sample. All these
systems show very high N(Ne VIII) (i.e. > 10^{15.6} cm^{-2}), high ionization
parameter (i.e. log U > 0.5), high metallicity (i.e. Z > Z_{\odot}), and
ionization potential dependent f_c values. The observed column density ratios
of different ions are reproduced by multiphase photoionization (PI) and/or
collisional ionization (CI) equilibrium models. While solar abundance ratios
are adequate in CIE, enhancement of Na relative to Mg is required in PI models
to explain our observations.
(Abridged) We present a sample of new population of associated absorbers,
detected through Ne VIII \lambda\lambda 770,780 absorption, in HST/COS spectra
of intermediate redshift (0.45 < z < 1.21) quasars (QSOs). Our sample comprised
of total 12 associated Ne VIII systems detected towards 8 lines of sight (none
of them are radio bright). The incidence rate of these absorbers is found to be
40%. Majority of the Ne VIII systems at small ejection velocities (v_ej) show
complete coverage of the background source, but systems with higher v_ej show
lower covering fractions (i.e. f_c < 0.8) and systematically higher values of
N(Ne VIII). We detect Mg X \lambda\lambda 609,624 absorption in 7 out of the 8
Ne VIII systems where the expected wavelength range is cover by our spectra and
is free of any strong blending. We report the detections of Na IX
\lambda\lambda 681,694 absorption, for the first time, in three highest
ejection velocity (e.g. v_ej > 7,000 km/s) systems in our sample. All these
systems show very high N(Ne VIII) (i.e. > 10^{15.6} cm^{-2}), high ionization
parameter (i.e. log U > 0.5), high metallicity (i.e. Z > Z_{\odot}), and
ionization potential dependent f_c values. The observed column density ratios
of different ions are reproduced by multiphase photoionization (PI) and/or
collisional ionization (CI) equilibrium models. While solar abundance ratios
are adequate in CIE, enhancement of Na relative to Mg is required in PI models
to explain our observations.
The Cluster and Field Galaxy AGN Fraction at z = 1 to 1.5: Evidence for a Reversal of the Local Anticorrelation Between Environment and AGN Fraction. (arXiv:1302.6253v1 [astro-ph.CO])
The Cluster and Field Galaxy AGN Fraction at z = 1 to 1.5: Evidence for a Reversal of the Local Anticorrelation Between Environment and AGN Fraction. (arXiv:1302.6253v1 [astro-ph.CO]):
The fraction of cluster galaxies that host luminous AGN is an important probe
of AGN fueling processes, the cold ISM at the centers of galaxies, and how
tightly black holes and galaxies co-evolve. We present a new measurement of the
AGN fraction in a sample of 13 clusters of galaxies (M >= 10^{14} Msun) at
1<z<1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the
field fraction in the immediate vicinity of these clusters, and combine these
data with measurements from the literature to quantify the relative evolution
of cluster and field AGN from the present to z~3. We estimate that the cluster
AGN fraction at 1<z<1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGN with a rest-frame,
hard X-ray luminosity greater than L_{X,H} >= 10^{44} erg/s. This fraction is
measured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1,
where M*_{3.6}(z) is the absolute magnitude of the break in the galaxy
luminosity function at the cluster redshift in the IRAC 3.6um bandpass. The
cluster AGN fraction is 30 times greater than the 3sigma upper limit on the
value for AGN of similar luminosity at z~0.25, as well as more than an order of
magnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} >= 10^{43}
erg/s exhibit similarly pronounced evolution with redshift. In contrast with
the local universe, where the luminous AGN fraction is higher in the field than
in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters
are consistent at 1<z<1.5. This is evidence that the cluster AGN population has
evolved more rapidly than the field population from z~1.5 to the present. This
environment-dependent AGN evolution mimics the more rapid evolution of
star-forming galaxies in clusters relative to the field.
The fraction of cluster galaxies that host luminous AGN is an important probe
of AGN fueling processes, the cold ISM at the centers of galaxies, and how
tightly black holes and galaxies co-evolve. We present a new measurement of the
AGN fraction in a sample of 13 clusters of galaxies (M >= 10^{14} Msun) at
1<z<1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the
field fraction in the immediate vicinity of these clusters, and combine these
data with measurements from the literature to quantify the relative evolution
of cluster and field AGN from the present to z~3. We estimate that the cluster
AGN fraction at 1<z<1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGN with a rest-frame,
hard X-ray luminosity greater than L_{X,H} >= 10^{44} erg/s. This fraction is
measured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1,
where M*_{3.6}(z) is the absolute magnitude of the break in the galaxy
luminosity function at the cluster redshift in the IRAC 3.6um bandpass. The
cluster AGN fraction is 30 times greater than the 3sigma upper limit on the
value for AGN of similar luminosity at z~0.25, as well as more than an order of
magnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} >= 10^{43}
erg/s exhibit similarly pronounced evolution with redshift. In contrast with
the local universe, where the luminous AGN fraction is higher in the field than
in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters
are consistent at 1<z<1.5. This is evidence that the cluster AGN population has
evolved more rapidly than the field population from z~1.5 to the present. This
environment-dependent AGN evolution mimics the more rapid evolution of
star-forming galaxies in clusters relative to the field.
A rapidly spinning supermassive black hole at the centre of NGC 1365. (arXiv:1302.7002v1 [astro-ph.HE])
A rapidly spinning supermassive black hole at the centre of NGC 1365. (arXiv:1302.7002v1 [astro-ph.HE]):
Broad X-ray emission lines from neutral and partially ionized iron observed
in active galaxies have been interpreted as fluorescence produced by the
reflection of hard X-rays off the inner edge of an accretion disk. In this
model, line broadening and distortion result from rapid rotation and
relativistic effects near the black hole, the line shape being sensitive to its
spin. Alternative models in which the distortions result from absorption by
intervening structures provide an equally good description of the data, and
there has been no general agreement on which is correct. Recent claims that the
black hole (2E6 solar masses) at the centre of the galaxy NGC 1365 is rotating
at close to its maximum possible speed rest on the assumption of relativistic
reflection. Here we report X-ray observations of NGC 1365 that reveal the
relativistic disk features through broadened Fe line emission and an associated
Compton scattering excess of 10-30 keV. Using temporal and spectral analyses,
we disentangle continuum changes due to time-variable absorption from
reflection, which we find arises from a region within 2.5 gravitational radii
of the rapidly spinning black hole. Absorption-dominated models that do not
include relativistic disk reflection can be ruled out both statistically and on
physical grounds.
Broad X-ray emission lines from neutral and partially ionized iron observed
in active galaxies have been interpreted as fluorescence produced by the
reflection of hard X-rays off the inner edge of an accretion disk. In this
model, line broadening and distortion result from rapid rotation and
relativistic effects near the black hole, the line shape being sensitive to its
spin. Alternative models in which the distortions result from absorption by
intervening structures provide an equally good description of the data, and
there has been no general agreement on which is correct. Recent claims that the
black hole (2E6 solar masses) at the centre of the galaxy NGC 1365 is rotating
at close to its maximum possible speed rest on the assumption of relativistic
reflection. Here we report X-ray observations of NGC 1365 that reveal the
relativistic disk features through broadened Fe line emission and an associated
Compton scattering excess of 10-30 keV. Using temporal and spectral analyses,
we disentangle continuum changes due to time-variable absorption from
reflection, which we find arises from a region within 2.5 gravitational radii
of the rapidly spinning black hole. Absorption-dominated models that do not
include relativistic disk reflection can be ruled out both statistically and on
physical grounds.
Probing the Extended Gaseous Regions of M31 with Quasar Absorption Lines. (arXiv:1302.7026v1 [astro-ph.CO])
Probing the Extended Gaseous Regions of M31 with Quasar Absorption Lines. (arXiv:1302.7026v1 [astro-ph.CO]):
We present HST-COS spectra of ten quasars located behind M31, selected to
investigate the properties of gas associated with its extended disk and high
velocity clouds (HVCs). The sightlines have impact parameters ranging between
b= 13 kpc and 112 kpc. No absorption is detected in the four sightlines beyond
b=57 kpc. Of the six remaining sightlines, all of which lie at b<32 kpc and
within the N(HI)= 2E18 cm^{-2} boundary of the HI disk of M31, we detect
low-ionization absorption at M31 velocities along four of them (three of which
include MgII absorption). We also detect MgII absorption from an HVC. We find
that along sightlines where both are detected, the velocity location of the
low-ion gas tracks the peak in 21 cm emission. High-ionization absorption is
detected along the three inner sightlines, but not along the three outer
sightlines, for which CIV data exist. As inferred from 21 cm emission line
maps, only one sightline may have a damped Ly-alpha system. This sightline has
b= 17.5 kpc, and we detect both low- and high-ion absorption lines associated
with it. It is the strongest single MgII2796 absorption line that we detect,
with W_0(2796)=0.63 A.
The impact parameters through M31 are similar to the impact parameters of
galaxies identified with MgII absorbers at redshifts 0.1<z<1.0 in a 2011 study
by Rao et al. However, the M31 MgII2796 rest equivalent width values are
significantly smaller. In comparison, moderate-to-strong MgII absorption from
Milky Way gas is detected along all ten sightlines. Thus, this study indicates
that M31 does not present itself as an absorbing galaxy which is typical of
higher-redshift galaxies inferred to give rise to moderate-strength quasar
absorption lines. M31 also appears not to possess an extensive large gaseous
cross section, at least not along the direction of its major axis. (Abridged.)
We present HST-COS spectra of ten quasars located behind M31, selected to
investigate the properties of gas associated with its extended disk and high
velocity clouds (HVCs). The sightlines have impact parameters ranging between
b= 13 kpc and 112 kpc. No absorption is detected in the four sightlines beyond
b=57 kpc. Of the six remaining sightlines, all of which lie at b<32 kpc and
within the N(HI)= 2E18 cm^{-2} boundary of the HI disk of M31, we detect
low-ionization absorption at M31 velocities along four of them (three of which
include MgII absorption). We also detect MgII absorption from an HVC. We find
that along sightlines where both are detected, the velocity location of the
low-ion gas tracks the peak in 21 cm emission. High-ionization absorption is
detected along the three inner sightlines, but not along the three outer
sightlines, for which CIV data exist. As inferred from 21 cm emission line
maps, only one sightline may have a damped Ly-alpha system. This sightline has
b= 17.5 kpc, and we detect both low- and high-ion absorption lines associated
with it. It is the strongest single MgII2796 absorption line that we detect,
with W_0(2796)=0.63 A.
The impact parameters through M31 are similar to the impact parameters of
galaxies identified with MgII absorbers at redshifts 0.1<z<1.0 in a 2011 study
by Rao et al. However, the M31 MgII2796 rest equivalent width values are
significantly smaller. In comparison, moderate-to-strong MgII absorption from
Milky Way gas is detected along all ten sightlines. Thus, this study indicates
that M31 does not present itself as an absorbing galaxy which is typical of
higher-redshift galaxies inferred to give rise to moderate-strength quasar
absorption lines. M31 also appears not to possess an extensive large gaseous
cross section, at least not along the direction of its major axis. (Abridged.)
Nuclear Masses and Neutron Stars. (arXiv:1303.1343v1 [nucl-th])
Nuclear Masses and Neutron Stars. (arXiv:1303.1343v1 [nucl-th]):
Precision mass spectrometry of neutron-rich nuclei is of great relevance for
astrophysics. Masses of exotic nuclides impose constraints on models for the
nuclear interaction and thus affect the description of the equation of state of
nuclear matter, which can be extended to describe neutron-star matter. With
knowledge of the masses of nuclides near shell closures, one can also derive
the neutron-star crustal composition. The Penning-trap mass spectrometer
ISOLTRAP at CERN-ISOLDE has recently achieved a breakthrough measuring the mass
of 82Zn, which allowed constraining neutron-star crust composition to deeper
layers (Wolf et al., PRL 110, 2013). We perform a more detailed study on the
sequence of nuclei in the outer crust of neutron stars with input from
different nuclear models to illustrate the sensitivity to masses and the
robustness of neutron-star models. The dominant role of the N=50 and N=82
closed neutron shells for the crustal composition is confirmed.
Precision mass spectrometry of neutron-rich nuclei is of great relevance for
astrophysics. Masses of exotic nuclides impose constraints on models for the
nuclear interaction and thus affect the description of the equation of state of
nuclear matter, which can be extended to describe neutron-star matter. With
knowledge of the masses of nuclides near shell closures, one can also derive
the neutron-star crustal composition. The Penning-trap mass spectrometer
ISOLTRAP at CERN-ISOLDE has recently achieved a breakthrough measuring the mass
of 82Zn, which allowed constraining neutron-star crust composition to deeper
layers (Wolf et al., PRL 110, 2013). We perform a more detailed study on the
sequence of nuclei in the outer crust of neutron stars with input from
different nuclear models to illustrate the sensitivity to masses and the
robustness of neutron-star models. The dominant role of the N=50 and N=82
closed neutron shells for the crustal composition is confirmed.
Saturday, March 9, 2013
Updates of the nuclear equation of state for core-collapse supernovae and neutron Stars: effects of 3-body forces, QCD, and magnetic fields. (arXiv:1302.5875v3 [astro-ph.HE] UPDATED)
Updates of the nuclear equation of state for core-collapse supernovae and neutron Stars: effects of 3-body forces, QCD, and magnetic fields. (arXiv:1302.5875v3 [astro-ph.HE] UPDATED):
We summarize several new developments in the nuclear equation of state for
supernova simulations and neutron stars. We discuss an updated and improved
Notre-Dame-Livermore Equation of State (NDL EoS) for use in supernovae
simulations. This Eos contains many updates. Among them are the effects of 3-
body nuclear forces at high densities and the possible transition to a QCD
chiral and/or super-conducting color phase at densities. We also consider the
neutron star equation of state and neutrino transport in the presence of strong
magnetic fields. We study a new quantum hadrodynamic (QHD) equation of state
for neutron stars (with and without hyperons) in the presence of strong
magnetic fields. The parameters are constrained by deduced masses and radii.
The calculated adiabatic index for these magnetized neutron stars exhibit rapid
changes with density. This may provide a mechanism for star-quakes and flares
in magnetars. We also investigate the strong magnetic field effects on the
moments of inertia and spin down of neutron stars. The change of the moment of
inertia associated with emitted magnetic flares is shown to match well with
observed glitches in some magnetars. We also discuss a perturbative calculation
of neutrino scattering and absorption in hot and dense hyperonic neutron-star
matter in the presence of a strong magnetic field. The absorption
cross-sections show a remarkable angular dependence in that the neutrino
absorption strength is reduced in a direction parallel to the magnetic field
and enhanced in the opposite direction. The pulsar kick velocities associated
with this asymmetry comparable to observed pulsar velocities and may affect the
early spin down rate of proto-neutron star magnetars with a toroidal field
configuration.
We summarize several new developments in the nuclear equation of state for
supernova simulations and neutron stars. We discuss an updated and improved
Notre-Dame-Livermore Equation of State (NDL EoS) for use in supernovae
simulations. This Eos contains many updates. Among them are the effects of 3-
body nuclear forces at high densities and the possible transition to a QCD
chiral and/or super-conducting color phase at densities. We also consider the
neutron star equation of state and neutrino transport in the presence of strong
magnetic fields. We study a new quantum hadrodynamic (QHD) equation of state
for neutron stars (with and without hyperons) in the presence of strong
magnetic fields. The parameters are constrained by deduced masses and radii.
The calculated adiabatic index for these magnetized neutron stars exhibit rapid
changes with density. This may provide a mechanism for star-quakes and flares
in magnetars. We also investigate the strong magnetic field effects on the
moments of inertia and spin down of neutron stars. The change of the moment of
inertia associated with emitted magnetic flares is shown to match well with
observed glitches in some magnetars. We also discuss a perturbative calculation
of neutrino scattering and absorption in hot and dense hyperonic neutron-star
matter in the presence of a strong magnetic field. The absorption
cross-sections show a remarkable angular dependence in that the neutrino
absorption strength is reduced in a direction parallel to the magnetic field
and enhanced in the opposite direction. The pulsar kick velocities associated
with this asymmetry comparable to observed pulsar velocities and may affect the
early spin down rate of proto-neutron star magnetars with a toroidal field
configuration.
A Super-Solar Metallicity for the Progenitor of Kepler's Supernova. (arXiv:1302.5435v2 [astro-ph.HE] UPDATED)
A Super-Solar Metallicity for the Progenitor of Kepler's Supernova. (arXiv:1302.5435v2 [astro-ph.HE] UPDATED):
We have performed deep X-ray observations of the remnant of Kepler's
supernova (SN 1604) as a Key Project of the Suzaku Observatory. Our main goal
is to detect secondary Fe-peak elements in the SN ejecta to gain insights into
the Type Ia supernova explosion mechanism and the nature of the progenitor.
Here we report our initial results. We made a conclusive detection of X-ray
emission lines from highly ionized Mn, Cr, and Ni as well as Fe. The observed
Mn-to-Cr line flux ratio is ~0.60, ~30% larger than that measured in Tycho's
remnant. We estimate a Mn-to-Cr mass ratio of ~0.77, which is strongly
suggestive of a large neutron excess in the progenitor star before the onset of
the thermonuclear runaway. The observed Ni-to-Fe line flux ratio (~0.03)
corresponds to a mass ratio of ~0.06, which is generally consistent with the
products of explosive Si-burning regime in Type Ia explosion models, and rules
out contamination from the products of neutron-rich nuclear statistical
equilibrium in the shocked ejecta. Together with the previously suggested
luminous nature of the explosion, these mass ratios provide strong evidence for
a super-solar metallicity in the SN progenitor (~3 Z_sun). Kepler's supernova
was likely the thermonuclear explosion of a white dwarf formed in the recent
past that must have exploded through a relatively prompt channel.
We have performed deep X-ray observations of the remnant of Kepler's
supernova (SN 1604) as a Key Project of the Suzaku Observatory. Our main goal
is to detect secondary Fe-peak elements in the SN ejecta to gain insights into
the Type Ia supernova explosion mechanism and the nature of the progenitor.
Here we report our initial results. We made a conclusive detection of X-ray
emission lines from highly ionized Mn, Cr, and Ni as well as Fe. The observed
Mn-to-Cr line flux ratio is ~0.60, ~30% larger than that measured in Tycho's
remnant. We estimate a Mn-to-Cr mass ratio of ~0.77, which is strongly
suggestive of a large neutron excess in the progenitor star before the onset of
the thermonuclear runaway. The observed Ni-to-Fe line flux ratio (~0.03)
corresponds to a mass ratio of ~0.06, which is generally consistent with the
products of explosive Si-burning regime in Type Ia explosion models, and rules
out contamination from the products of neutron-rich nuclear statistical
equilibrium in the shocked ejecta. Together with the previously suggested
luminous nature of the explosion, these mass ratios provide strong evidence for
a super-solar metallicity in the SN progenitor (~3 Z_sun). Kepler's supernova
was likely the thermonuclear explosion of a white dwarf formed in the recent
past that must have exploded through a relatively prompt channel.
Validity of Hydrostatic Equilibrium in Galaxy Clusters from Cosmological Hydrodynamical Simulations. (arXiv:1302.5172v1 [astro-ph.CO])
Validity of Hydrostatic Equilibrium in Galaxy Clusters from Cosmological Hydrodynamical Simulations. (arXiv:1302.5172v1 [astro-ph.CO]):
We examine the validity of the hydrostatic equilibrium (HSE) assumption for
galaxy clusters using one of the highest-resolution cosmological hydrodynamical
simulations. We define and evaluate several effective mass terms corresponding
to the Euler equations of the gas dynamics, and quantify the degree of the
validity of HSE in terms of the mass estimate. We find that the mass estimated
under the HSE assumption (the HSE mass) deviates from the true mass by up to ~
30 %. This level of departure from HSE is consistent with the previous claims,
but our physical interpretation is rather different. We demonstrate that the
inertial term in the Euler equations makes a negligible contribution to the
total mass, and the overall gravity of the cluster is balanced by the thermal
gas pressure gradient and the gas acceleration term. Indeed the deviation from
the HSE mass is well explained by the acceleration term at almost all radii. We
also clarify the confusion of previous work due to the inappropriate
application of the Jeans equations in considering the validity of HSE from the
gas dynamics extracted from cosmological hydrodynamical simulations.
We examine the validity of the hydrostatic equilibrium (HSE) assumption for
galaxy clusters using one of the highest-resolution cosmological hydrodynamical
simulations. We define and evaluate several effective mass terms corresponding
to the Euler equations of the gas dynamics, and quantify the degree of the
validity of HSE in terms of the mass estimate. We find that the mass estimated
under the HSE assumption (the HSE mass) deviates from the true mass by up to ~
30 %. This level of departure from HSE is consistent with the previous claims,
but our physical interpretation is rather different. We demonstrate that the
inertial term in the Euler equations makes a negligible contribution to the
total mass, and the overall gravity of the cluster is balanced by the thermal
gas pressure gradient and the gas acceleration term. Indeed the deviation from
the HSE mass is well explained by the acceleration term at almost all radii. We
also clarify the confusion of previous work due to the inappropriate
application of the Jeans equations in considering the validity of HSE from the
gas dynamics extracted from cosmological hydrodynamical simulations.
Can AGN feedback-driven star formation explain the size evolution of massive galaxies?. (arXiv:1302.4998v1 [astro-ph.GA])
Can AGN feedback-driven star formation explain the size evolution of massive galaxies?. (arXiv:1302.4998v1 [astro-ph.GA]):
Observations indicate that massive galaxies at z~2 are more compact than
galaxies of comparable mass at z~0, with effective radii evolving by a factor
of ~3-5. This implies that galaxies grow significantly in size but relatively
little in mass over the past ~10 Gyr. Two main physical models have been
proposed in order to explain the observed evolution of massive galaxies:
"mergers" and "puffing-up" scenarios. Here we introduce another possibility,
and discuss the potential role of the central active galactic nucleus (AGN)
feedback on the evolution of its host galaxy. We consider triggering of star
formation, due to AGN feedback, with radiation pressure on dusty gas as the
driving feedback mechanism. In this picture, stars are formed in the
feedback-driven outflow at increasingly larger radii and build up the outer
regions of the host galaxy. The resulting increase in size and stellar mass can
be compared with the observed growth of massive galaxies. Star formation in the
host galaxy is likely obscured due to dust extinction and reddening. We suggest
a number of observational predictions of our model, and discuss possible
implications for AGN feedback-driven star formation.
Observations indicate that massive galaxies at z~2 are more compact than
galaxies of comparable mass at z~0, with effective radii evolving by a factor
of ~3-5. This implies that galaxies grow significantly in size but relatively
little in mass over the past ~10 Gyr. Two main physical models have been
proposed in order to explain the observed evolution of massive galaxies:
"mergers" and "puffing-up" scenarios. Here we introduce another possibility,
and discuss the potential role of the central active galactic nucleus (AGN)
feedback on the evolution of its host galaxy. We consider triggering of star
formation, due to AGN feedback, with radiation pressure on dusty gas as the
driving feedback mechanism. In this picture, stars are formed in the
feedback-driven outflow at increasingly larger radii and build up the outer
regions of the host galaxy. The resulting increase in size and stellar mass can
be compared with the observed growth of massive galaxies. Star formation in the
host galaxy is likely obscured due to dust extinction and reddening. We suggest
a number of observational predictions of our model, and discuss possible
implications for AGN feedback-driven star formation.
RX J0648.0--4418: the fastest-spinning white dwarf. (arXiv:1302.4634v1 [astro-ph.HE])
RX J0648.0--4418: the fastest-spinning white dwarf. (arXiv:1302.4634v1 [astro-ph.HE]):
RX J0648.0-4418 is a post common-envelope X-ray binary composed of a hot
subdwarf and one of the most massive white dwarfs with a dynamical mass
measurement (1.28+/-0.05 M_sun). This white dwarf, with a spin period of 13.2
s, rotates more than twice faster than the white dwarf in the cataclysmic
variable AE Aqr. The current properties of these two binaries, as well as their
future evolution, are quite different, despite both contain a fast-spinning
white dwarf. RX J0648.0-4418 could be the progenitor of either a Type Ia
supernova or of a non-recycled millisecond pulsars.
RX J0648.0-4418 is a post common-envelope X-ray binary composed of a hot
subdwarf and one of the most massive white dwarfs with a dynamical mass
measurement (1.28+/-0.05 M_sun). This white dwarf, with a spin period of 13.2
s, rotates more than twice faster than the white dwarf in the cataclysmic
variable AE Aqr. The current properties of these two binaries, as well as their
future evolution, are quite different, despite both contain a fast-spinning
white dwarf. RX J0648.0-4418 could be the progenitor of either a Type Ia
supernova or of a non-recycled millisecond pulsars.
A CR-hydro-NEI Model of Multi-wavelength Emission from the Vela Jr. Supernova Remnant (SNR RX J0852.0-4622). (arXiv:1302.4645v1 [astro-ph.HE])
A CR-hydro-NEI Model of Multi-wavelength Emission from the Vela Jr. Supernova Remnant (SNR RX J0852.0-4622). (arXiv:1302.4645v1 [astro-ph.HE]):
Based largely on energy budget considerations and the observed cosmic-ray
(CR) ionic composition, supernova remnant (SNR) blast waves are the most likely
sources of CR ions with energies at least up to the "knee" near 3 PeV. Shocks
in young shell-type TeV-bright SNRs are surely producing TeV particles, but the
emission could be dominated by ions producing neutral pion-decay emission or
electrons producing inverse-Compton gamma-rays. Unambiguously identifying the
GeV-TeV emission process in a particular SNR will not only help pin down the
origin of CRs, it will add significantly to our understanding of the diffusive
shock acceleration (DSA) mechanism and improve our understanding of supernovae
and the impact SNRs have on the circumstellar medium. In this study, we
investigate the Vela Jr. SNR, an example of TeV-bright non-thermal SNRs. We
perform hydrodynamic simulations coupled with non-linear DSA and
non-equilibrium ionization near the forward shock (FS) to confront currently
available multi-wavelength data. We find, with an analysis similar to that used
earlier for SNR RX J1713.7-3946, that self-consistently modeling the thermal
X-ray line emission with the non-thermal continuum in our one-dimensional model
strongly constrains the fitting parameters, and this leads convincingly to a
leptonic origin for the GeV-TeV emission for Vela Jr. This conclusion is
further supported by applying additional constraints from observation,
including the radial brightness profiles of the SNR shell in TeV gamma-rays,
and the spatial variation of the X-ray synchrotron spectral index. We will
discuss implications of our models on future observations by the
next-generation telescopes.
Based largely on energy budget considerations and the observed cosmic-ray
(CR) ionic composition, supernova remnant (SNR) blast waves are the most likely
sources of CR ions with energies at least up to the "knee" near 3 PeV. Shocks
in young shell-type TeV-bright SNRs are surely producing TeV particles, but the
emission could be dominated by ions producing neutral pion-decay emission or
electrons producing inverse-Compton gamma-rays. Unambiguously identifying the
GeV-TeV emission process in a particular SNR will not only help pin down the
origin of CRs, it will add significantly to our understanding of the diffusive
shock acceleration (DSA) mechanism and improve our understanding of supernovae
and the impact SNRs have on the circumstellar medium. In this study, we
investigate the Vela Jr. SNR, an example of TeV-bright non-thermal SNRs. We
perform hydrodynamic simulations coupled with non-linear DSA and
non-equilibrium ionization near the forward shock (FS) to confront currently
available multi-wavelength data. We find, with an analysis similar to that used
earlier for SNR RX J1713.7-3946, that self-consistently modeling the thermal
X-ray line emission with the non-thermal continuum in our one-dimensional model
strongly constrains the fitting parameters, and this leads convincingly to a
leptonic origin for the GeV-TeV emission for Vela Jr. This conclusion is
further supported by applying additional constraints from observation,
including the radial brightness profiles of the SNR shell in TeV gamma-rays,
and the spatial variation of the X-ray synchrotron spectral index. We will
discuss implications of our models on future observations by the
next-generation telescopes.
Discovery of a 168.8 s X-ray pulsar transiting in front of its Be companion star in the Large Magellanic Cloud. (arXiv:1302.4665v1 [astro-ph.HE])
Discovery of a 168.8 s X-ray pulsar transiting in front of its Be companion star in the Large Magellanic Cloud. (arXiv:1302.4665v1 [astro-ph.HE]):
Aims: We report the discovery of LXP169, a new high-mass X-ray binary in the
Large Magellanic Cloud. The optical counterpart is identified and exhibits an
eclipsing light curve. We performed follow-up observations to clarify the
eclipsing nature of the system. Methods: Energy spectra and time series were
extracted from two XMM-Newton observations to search for pulsations,
characterise the spectrum and measure spectral and timing changes. Long-term
X-ray variability was studied using archival ROSAT data. The XMM-Newton
positions were used to identify the optical counterpart. We obtained
ultraviolet to near-infrared photometry to characterise the companion, along
with its 4000 d long I-band light curve. We observed LXP169 with Swift at two
predicted eclipse times. Results: We found a spin period of 168.8 s which did
not change between two XMM-Newton observations. The X-ray spectrum, well
characterised by a power-law, was harder when the source was brighter. The
X-ray flux of LXP169 is found to be variable by a factor of at least 10. The
counterpart is highly variable on short and long timescales, and its photometry
is that of an early-type star with a near-infrared excess. This classifies the
source as a Be/X-ray binary pulsar. We observed a transit in the ultraviolet,
thereby confirming that the companion star itself is eclipsed. We give an
ephemeris for the transit of MJD56203.877(-0.197,+0.934)+N*(24.329+/-0.008). We
propose and discuss the scenario where the matter captured from the companion's
equatorial disc creates an extended region of high density around the neutron
star, which partially eclipses the companion as the neutron star transits in
front of it. Conclusions: LXP169 is the first confirmed eclipsing Be/X-ray
binary. For the first time we observe the compact object in an X-ray binary
eclipsing its companion star, and much can be learned by studying this
important system.
Aims: We report the discovery of LXP169, a new high-mass X-ray binary in the
Large Magellanic Cloud. The optical counterpart is identified and exhibits an
eclipsing light curve. We performed follow-up observations to clarify the
eclipsing nature of the system. Methods: Energy spectra and time series were
extracted from two XMM-Newton observations to search for pulsations,
characterise the spectrum and measure spectral and timing changes. Long-term
X-ray variability was studied using archival ROSAT data. The XMM-Newton
positions were used to identify the optical counterpart. We obtained
ultraviolet to near-infrared photometry to characterise the companion, along
with its 4000 d long I-band light curve. We observed LXP169 with Swift at two
predicted eclipse times. Results: We found a spin period of 168.8 s which did
not change between two XMM-Newton observations. The X-ray spectrum, well
characterised by a power-law, was harder when the source was brighter. The
X-ray flux of LXP169 is found to be variable by a factor of at least 10. The
counterpart is highly variable on short and long timescales, and its photometry
is that of an early-type star with a near-infrared excess. This classifies the
source as a Be/X-ray binary pulsar. We observed a transit in the ultraviolet,
thereby confirming that the companion star itself is eclipsed. We give an
ephemeris for the transit of MJD56203.877(-0.197,+0.934)+N*(24.329+/-0.008). We
propose and discuss the scenario where the matter captured from the companion's
equatorial disc creates an extended region of high density around the neutron
star, which partially eclipses the companion as the neutron star transits in
front of it. Conclusions: LXP169 is the first confirmed eclipsing Be/X-ray
binary. For the first time we observe the compact object in an X-ray binary
eclipsing its companion star, and much can be learned by studying this
important system.
Monday, March 4, 2013
Quasar Absorption Lines in the Far Ultraviolet: An Untapped Gold Mine for Galaxy Evolution Studies. (arXiv:1303.0043v1 [astro-ph.CO])
Quasar Absorption Lines in the Far Ultraviolet: An Untapped Gold Mine for Galaxy Evolution Studies. (arXiv:1303.0043v1 [astro-ph.CO]):
This white paper emphasizes the potential of QSO absorption lines in the
rest-frame far/extreme UV at rest-frame wavelengths from ~500 to 2000 A. In
this wavelength range, species such as Ne VIII, Na IX, and Mg X can be
detected, providing diagnostics of gas with temperatures >> 10^{6} K, as well
as banks of adjacent ions such as O I, O II, O III, O IV, O V, and O VI (and
similarly N I - N V; S II - S VI; Ne II - Ne VIII, etc.), which constrain
physical conditions with unprecedented precision. A UV spectrograph with good
sensitivity down to observed wavelengths of 1000 A can detect these new probes
in absorption systems with redshift z(abs) > 0.3, and at these redshifts, the
detailed relationships between the absorbers and nearby galaxies and
large-scale environment can be studied from the ground. By observing QSOs at z
= 1.0 - 1.5, HST has started to exploit extreme-UV QSO absorption lines, but
HST can only reach a small number of these targets. A future, more sensitive UV
spectrograph could open up this new discovery space.
This white paper emphasizes the potential of QSO absorption lines in the
rest-frame far/extreme UV at rest-frame wavelengths from ~500 to 2000 A. In
this wavelength range, species such as Ne VIII, Na IX, and Mg X can be
detected, providing diagnostics of gas with temperatures >> 10^{6} K, as well
as banks of adjacent ions such as O I, O II, O III, O IV, O V, and O VI (and
similarly N I - N V; S II - S VI; Ne II - Ne VIII, etc.), which constrain
physical conditions with unprecedented precision. A UV spectrograph with good
sensitivity down to observed wavelengths of 1000 A can detect these new probes
in absorption systems with redshift z(abs) > 0.3, and at these redshifts, the
detailed relationships between the absorbers and nearby galaxies and
large-scale environment can be studied from the ground. By observing QSOs at z
= 1.0 - 1.5, HST has started to exploit extreme-UV QSO absorption lines, but
HST can only reach a small number of these targets. A future, more sensitive UV
spectrograph could open up this new discovery space.
The NDL Equation of State for Supernova Simulations. (arXiv:1303.0064v1 [astro-ph.HE])
The NDL Equation of State for Supernova Simulations. (arXiv:1303.0064v1 [astro-ph.HE]):
We present an updated and improved equation of state (which we call the NDL
EoS) for use in neutron-star structure and supernova simulations. This EoS is
based upon a framework originally developed by Bowers & Wilson, but there are
numerous changes. Among them are: (1) a reformulation in the context of density
functional theory; (2) the possibility of the formation of material with a net
proton excess (Ye > 0.5); (3) an improved treatment of the nuclear statistical
equilibrium and the transition to heavy nuclei as the density approaches
nuclear matter density; (4) an improved treatment of the effects of pions in
the regime above nuclear matter density including the incorporation of all the
known mesonic and baryonic states at high temperature; (5) the effects of
3-body nuclear forces at high densities; and (6) the possibility of a
first-order or crossover transition to a QCD chiral symmetry restoration and
deconfinement phase at densities above nuclear matter density. This paper
details the physics of, and constraints on, this new EoS and describes its
implementation in numerical simulations. We show comparisons of this EoS with
other equations of state commonly used in supernova collapse simulations.
We present an updated and improved equation of state (which we call the NDL
EoS) for use in neutron-star structure and supernova simulations. This EoS is
based upon a framework originally developed by Bowers & Wilson, but there are
numerous changes. Among them are: (1) a reformulation in the context of density
functional theory; (2) the possibility of the formation of material with a net
proton excess (Ye > 0.5); (3) an improved treatment of the nuclear statistical
equilibrium and the transition to heavy nuclei as the density approaches
nuclear matter density; (4) an improved treatment of the effects of pions in
the regime above nuclear matter density including the incorporation of all the
known mesonic and baryonic states at high temperature; (5) the effects of
3-body nuclear forces at high densities; and (6) the possibility of a
first-order or crossover transition to a QCD chiral symmetry restoration and
deconfinement phase at densities above nuclear matter density. This paper
details the physics of, and constraints on, this new EoS and describes its
implementation in numerical simulations. We show comparisons of this EoS with
other equations of state commonly used in supernova collapse simulations.
Sunday, March 3, 2013
Conditions For Successful Helium Detonations In Astrophysical Environments. (arXiv:1302.6235v1 [astro-ph.HE])
Conditions For Successful Helium Detonations In Astrophysical Environments. (arXiv:1302.6235v1 [astro-ph.HE]):
Several models for type Ia-like supernovae events rely on the production of a
self-sustained detonation powered by nuclear reactions.In the absence of
hydrogen, the fuel that powers these detonations typically consists of either
pure helium (He) or a mixture of carbon and oxygen (C/O). Studies that
systematically determine the conditions required to initiate detonations in C/O
material exist, but until now no analogous investigation of degenerate He
matter has been conducted. We perform one-dimensional reactive hydrodynamical
simulations at a variety of initial density and temperature combinations and
find critical length scales for the initiation of He detonations that range
between 1 -- $10^{10}$ cm. These sizes are consistently smaller than the
corresponding Chapman-Jouguet (CJ) length scales by a factor of ~100, providing
opportunities for thermonuclear explosions in a wider range of low mass white
dwarfs (WDs) than previously thought possible. We find that virialized WDs with
as little mass as 0.24 $M_\odot$ can be detonated, and that even less massive
WDs can be detonated if a sizable fraction of their mass is raised to a higher
adiabat. That the initiation length is exceeded by the CJ length implies that
certain systems may not reach nuclear statistical equilibrium within the time
it takes a detonation to traverse the object. In support of this hypothesis, we
demonstrate that incomplete burning will occur in the majority of He WD
detonations and that $^{44}$Ti, rather than $^{56}$Ni, is the predominant
burning product for many of these events. We anticipate that a measure of the
quantity of $^{44}$Ti and $^{56}$Ni produced in a helium-rich thermonuclear
explosion can potentially be used to constrain the nature of the progenitor
system.
Several models for type Ia-like supernovae events rely on the production of a
self-sustained detonation powered by nuclear reactions.In the absence of
hydrogen, the fuel that powers these detonations typically consists of either
pure helium (He) or a mixture of carbon and oxygen (C/O). Studies that
systematically determine the conditions required to initiate detonations in C/O
material exist, but until now no analogous investigation of degenerate He
matter has been conducted. We perform one-dimensional reactive hydrodynamical
simulations at a variety of initial density and temperature combinations and
find critical length scales for the initiation of He detonations that range
between 1 -- $10^{10}$ cm. These sizes are consistently smaller than the
corresponding Chapman-Jouguet (CJ) length scales by a factor of ~100, providing
opportunities for thermonuclear explosions in a wider range of low mass white
dwarfs (WDs) than previously thought possible. We find that virialized WDs with
as little mass as 0.24 $M_\odot$ can be detonated, and that even less massive
WDs can be detonated if a sizable fraction of their mass is raised to a higher
adiabat. That the initiation length is exceeded by the CJ length implies that
certain systems may not reach nuclear statistical equilibrium within the time
it takes a detonation to traverse the object. In support of this hypothesis, we
demonstrate that incomplete burning will occur in the majority of He WD
detonations and that $^{44}$Ti, rather than $^{56}$Ni, is the predominant
burning product for many of these events. We anticipate that a measure of the
quantity of $^{44}$Ti and $^{56}$Ni produced in a helium-rich thermonuclear
explosion can potentially be used to constrain the nature of the progenitor
system.
The AD775 cosmic event revisited: the Sun is to blame. (arXiv:1302.6897v1 [astro-ph.SR])
The AD775 cosmic event revisited: the Sun is to blame. (arXiv:1302.6897v1 [astro-ph.SR]):
Miyake et al. (henceforth M12) recently reported, based on 14C data, an
extreme cosmic event ca. AD775. Using a simple model, M12 claimed that the
event was too strong to be caused by a solar flare within the standard theory.
This implied a new paradigm of either an impossibly strong solar flare or a
very strong cosmic ray event of unknown origin occurred ca. AD775. We show that
the strength of the event was significantly overestimated by M12. Several
subsequent works have attempted to find a possible exotic source for such an
event, but they are all based on incorrect estimates by M12. We revisit this
event with analysis of new datasets and consistent theoretical modelling. We
verified the experimental result for the AD775 event using independent datasets
including 10Be series and newly measured 14C annual data. We surveyed available
historical chronicles for astronomical observations for the AD770s to identify
potential sightings of aurorae or supernovae. We interpreted the 14C
measurements using an appropriate carbon cycle model. We show that: (1) The
reality of the AD775 event is confirmed by new measurements of 14C; (2) by
using an inappropriate carbon cycle model, M12 strongly overestimated the
event's strength; (3) The revised magnitude of the event is consistent with
different independent datasets (14C, 10Be, 36Cl) and can be associated with a
strong, but not inexplicably strong, SEP event (or a sequence of events), and
provides the first evidence for an event of this magnitude (the fluence >30 MeV
was about 4.5*10^{10} /cm2) in multiple datasets; (4) This is in agreement with
increased auroral activity identified in historical chronicles. This point to
the likely solar origin of the event, which is the greatest solar event on a
multi-millennial time scale, placing a strong observational constraint on the
theory of explosive energy releases on the Sun and cool stars.
Miyake et al. (henceforth M12) recently reported, based on 14C data, an
extreme cosmic event ca. AD775. Using a simple model, M12 claimed that the
event was too strong to be caused by a solar flare within the standard theory.
This implied a new paradigm of either an impossibly strong solar flare or a
very strong cosmic ray event of unknown origin occurred ca. AD775. We show that
the strength of the event was significantly overestimated by M12. Several
subsequent works have attempted to find a possible exotic source for such an
event, but they are all based on incorrect estimates by M12. We revisit this
event with analysis of new datasets and consistent theoretical modelling. We
verified the experimental result for the AD775 event using independent datasets
including 10Be series and newly measured 14C annual data. We surveyed available
historical chronicles for astronomical observations for the AD770s to identify
potential sightings of aurorae or supernovae. We interpreted the 14C
measurements using an appropriate carbon cycle model. We show that: (1) The
reality of the AD775 event is confirmed by new measurements of 14C; (2) by
using an inappropriate carbon cycle model, M12 strongly overestimated the
event's strength; (3) The revised magnitude of the event is consistent with
different independent datasets (14C, 10Be, 36Cl) and can be associated with a
strong, but not inexplicably strong, SEP event (or a sequence of events), and
provides the first evidence for an event of this magnitude (the fluence >30 MeV
was about 4.5*10^{10} /cm2) in multiple datasets; (4) This is in agreement with
increased auroral activity identified in historical chronicles. This point to
the likely solar origin of the event, which is the greatest solar event on a
multi-millennial time scale, placing a strong observational constraint on the
theory of explosive energy releases on the Sun and cool stars.
Saturday, March 2, 2013
The progenitor of SN 2011ja: Clues from circumstellar interaction. (arXiv:1302.7067v1 [astro-ph.HE])
The progenitor of SN 2011ja: Clues from circumstellar interaction. (arXiv:1302.7067v1 [astro-ph.HE]):
Massive stars, possibly red supergiants, which retain extended hydrogen
envelopes until the time of core collapse produce Type IIP (Plateau)
supernovae. The ejecta from these explosions shock the circumstellar matter
originating from the mass loss of the progenitor during the final phases of its
life. This interaction accelerates particles to relativistic energies which
then lose energy via synchrotron radiation in the shock-amplified magnetic
fields and inverse Compton scattering against optical photons from the
supernova. These processes produce different signatures in the radio and X-ray
part of the electromagnetic spectrum. Observed together, they allow us to break
the degeneracy between shock acceleration and magnetic field amplification. In
this work we use X-rays observations from the Chandra and radio observations
from the ATCA to study the relative importance of particle acceleration and
magnetic fields in producing the non-thermal radiation from SN 2011ja. We use
radio observations to constrain the explosion date. Multiple Chandra
observations allow us to probe the history of variable mass loss from the
progenitor. The ejecta expands into a low density bubble followed by
interaction with a higher density wind from a red supergiant consistent with
M>16 solar masses. Our results suggest that a fraction of type IIP supernovae
may interact with circumstellar media set up by non-steady winds.
Massive stars, possibly red supergiants, which retain extended hydrogen
envelopes until the time of core collapse produce Type IIP (Plateau)
supernovae. The ejecta from these explosions shock the circumstellar matter
originating from the mass loss of the progenitor during the final phases of its
life. This interaction accelerates particles to relativistic energies which
then lose energy via synchrotron radiation in the shock-amplified magnetic
fields and inverse Compton scattering against optical photons from the
supernova. These processes produce different signatures in the radio and X-ray
part of the electromagnetic spectrum. Observed together, they allow us to break
the degeneracy between shock acceleration and magnetic field amplification. In
this work we use X-rays observations from the Chandra and radio observations
from the ATCA to study the relative importance of particle acceleration and
magnetic fields in producing the non-thermal radiation from SN 2011ja. We use
radio observations to constrain the explosion date. Multiple Chandra
observations allow us to probe the history of variable mass loss from the
progenitor. The ejecta expands into a low density bubble followed by
interaction with a higher density wind from a red supergiant consistent with
M>16 solar masses. Our results suggest that a fraction of type IIP supernovae
may interact with circumstellar media set up by non-steady winds.
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