The Nuclear Equation of State and Neutron Star Masses. (arXiv:1305.3510v1 [nucl-th]):
Neutron stars are valuable laboratories for the study of dense matter. Recent
observations have uncovered both massive and low-mass neutron stars and have
also set constraints on neutron star radii. The largest mass measurements are
powerfully influencing the high-density equation of state because of the
existence of the neutron star maximum mass. The smallest mass measurements, and
the distributions of masses, have implications for the progenitors and
formation mechanisms of neutron stars. The ensemble of mass and radius
observations can realistically restrict the properties of dense matter, and, in
particular, the behavior of the nuclear symmetry energy near the nuclear
saturation density. Simultaneously, various nuclear experiments are
progressively restricting the ranges of parameters describing the symmetry
properties of the nuclear equation of state. In addition, new theoretical
studies of pure neutron matter are providing insights. These observational,
experimental and theoretical constraints of dense matter, when combined, are
now revealing a remarkable convergence.
Wednesday, May 15, 2013
A Decade-Baseline Study of the Plasma States of Ejecta Knots in Cassiopeia A. (arXiv:1305.1581v1 [astro-ph.HE])
A Decade-Baseline Study of the Plasma States of Ejecta Knots in Cassiopeia A. (arXiv:1305.1581v1 [astro-ph.HE]):
We present the analysis of 21 bright X-ray knots in the Cassiopeia A
supernova remnant from observations spanning 10 yr. We performed a
comprehensive set of measurements to reveal the kinematic and thermal state of
the plasma in each knot, using a combined analysis of two high energy
resolution High Energy Transmission Grating (HETG) and four medium energy
resolution Advanced CCD Imaging Spectrometer (ACIS) sets of spectra. The ACIS
electron temperature estimates agree with the HETG-derived values for
approximately half of the knots studied, yielding one of the first comparisons
between high resolution temperature estimates and ACIS-derived temperatures. We
did not observe the expected spectral evolutionpredicted from the ionization
age and density estimates for each knotin all but three of the knots studied.
The incompatibility of these measurements with our assumptions has led us to
propose a dissociated ejecta model, with the metals unmixed inside the knots,
which could place strong constraints on supernova mixing models.
We present the analysis of 21 bright X-ray knots in the Cassiopeia A
supernova remnant from observations spanning 10 yr. We performed a
comprehensive set of measurements to reveal the kinematic and thermal state of
the plasma in each knot, using a combined analysis of two high energy
resolution High Energy Transmission Grating (HETG) and four medium energy
resolution Advanced CCD Imaging Spectrometer (ACIS) sets of spectra. The ACIS
electron temperature estimates agree with the HETG-derived values for
approximately half of the knots studied, yielding one of the first comparisons
between high resolution temperature estimates and ACIS-derived temperatures. We
did not observe the expected spectral evolutionpredicted from the ionization
age and density estimates for each knotin all but three of the knots studied.
The incompatibility of these measurements with our assumptions has led us to
propose a dissociated ejecta model, with the metals unmixed inside the knots,
which could place strong constraints on supernova mixing models.
Constraints on black hole fuelling modes from the clustering of X-ray AGN. (arXiv:1305.2200v1 [astro-ph.CO])
Constraints on black hole fuelling modes from the clustering of X-ray AGN. (arXiv:1305.2200v1 [astro-ph.CO]):
We present a clustering analysis of X-ray selected AGN by compiling X-ray
samples from the literature and re-estimating the dark matter (DM) halo masses
of AGN in a uniform manner. We find that moderate luminosity AGN (Lx(2-10
keV)=10^42-10^44 erg/sec) in the z=0-1.3 Universe are typically found in DM
haloes with masses of ~10^13 Msun. We then compare our findings to the
theoretical predictions of the coupled galaxy and black hole formation model
GALFORM. We find good agreement when our calculation includes the hot-halo mode
of accretion onto the central black hole. This type of accretion, which is
additional to the common cold accretion during disk instabilities and galaxy
mergers, is tightly coupled to the AGN feedback in the model. The hot-halo mode
becomes prominent in DM haloes with masses greater than ~10^12.5 Msun, where
AGN feedback typically operates, giving rise to a distinct class of moderate
luminosity AGN that inhabit rich clusters and superclusters. Cold gas fuelling
of the black hole cannot produce the observationally inferred DM halo masses of
X-ray AGN. Switching off AGN feedback in the model results in a large
population of luminous quasars (Lx(2-10 keV) > 10^44 erg/sec) in DM haloes with
masses up to ~10^14 Msun, which is inconsistent with the observed clustering of
quasars. The abundance of hot-halo AGN decreases significantly in the z~3-4
universe. At such high redshifts, the cold accretion mode is solely responsible
for shaping the environment of moderate luminosity AGN. Our analysis supports
two accretion modes (cold and hot) for the fuelling of supermassive black holes
and strongly underlines the importance of AGN feedback in cosmological models
both of galaxy formation and black hole growth.
We present a clustering analysis of X-ray selected AGN by compiling X-ray
samples from the literature and re-estimating the dark matter (DM) halo masses
of AGN in a uniform manner. We find that moderate luminosity AGN (Lx(2-10
keV)=10^42-10^44 erg/sec) in the z=0-1.3 Universe are typically found in DM
haloes with masses of ~10^13 Msun. We then compare our findings to the
theoretical predictions of the coupled galaxy and black hole formation model
GALFORM. We find good agreement when our calculation includes the hot-halo mode
of accretion onto the central black hole. This type of accretion, which is
additional to the common cold accretion during disk instabilities and galaxy
mergers, is tightly coupled to the AGN feedback in the model. The hot-halo mode
becomes prominent in DM haloes with masses greater than ~10^12.5 Msun, where
AGN feedback typically operates, giving rise to a distinct class of moderate
luminosity AGN that inhabit rich clusters and superclusters. Cold gas fuelling
of the black hole cannot produce the observationally inferred DM halo masses of
X-ray AGN. Switching off AGN feedback in the model results in a large
population of luminous quasars (Lx(2-10 keV) > 10^44 erg/sec) in DM haloes with
masses up to ~10^14 Msun, which is inconsistent with the observed clustering of
quasars. The abundance of hot-halo AGN decreases significantly in the z~3-4
universe. At such high redshifts, the cold accretion mode is solely responsible
for shaping the environment of moderate luminosity AGN. Our analysis supports
two accretion modes (cold and hot) for the fuelling of supermassive black holes
and strongly underlines the importance of AGN feedback in cosmological models
both of galaxy formation and black hole growth.
Turbulence in the SuperModel: Mass Reconstruction with Nonthermal Pressure for Abell 1835. (arXiv:1305.3020v1 [astro-ph.CO])
Turbulence in the SuperModel: Mass Reconstruction with Nonthermal Pressure for Abell 1835. (arXiv:1305.3020v1 [astro-ph.CO]):
The total mass derived from X-ray emission is biased low in a large number of
clusters when compared with the mass estimated via strong and weak lensing.
Suzaku and Chandra observations out to the virial radius report in several
relaxed clusters steep temperature gradients that on assuming pure thermal
hydrostatic equilibrium imply an unphysically decreasing mass profile.
Moreover, the gas mass fraction appears to be inconsistent with the cosmic
value measured from the CMB. Such findings can be interpreted as an evidence
for an additional nonthermal pressure in the outskirts of these clusters. This
nonthermal component may be due to turbulence stirred by residual bulk motions
of extragalactic gas infalling into the cluster. Here we present a SuperModel
analysis of Abell 1835 observed by Chandra out to the virial radius. The
SuperModel formalism can include in the equilibrium a nonthermal component
whose level and distribution are derived imposing that the gas mass fraction
f_{gas} equals the cosmic value at the virial radius. Including such a
nonthermal component, we reconstruct from X rays an increasing mass profile
consistent with the hydrostatic equilibrium also in the cluster outskirts and
in agreement at the virial boundary with the weak lensing value. The increasing
f_{gas} profile confirms that the baryons are not missing but located at the
cluster outskirts.
The total mass derived from X-ray emission is biased low in a large number of
clusters when compared with the mass estimated via strong and weak lensing.
Suzaku and Chandra observations out to the virial radius report in several
relaxed clusters steep temperature gradients that on assuming pure thermal
hydrostatic equilibrium imply an unphysically decreasing mass profile.
Moreover, the gas mass fraction appears to be inconsistent with the cosmic
value measured from the CMB. Such findings can be interpreted as an evidence
for an additional nonthermal pressure in the outskirts of these clusters. This
nonthermal component may be due to turbulence stirred by residual bulk motions
of extragalactic gas infalling into the cluster. Here we present a SuperModel
analysis of Abell 1835 observed by Chandra out to the virial radius. The
SuperModel formalism can include in the equilibrium a nonthermal component
whose level and distribution are derived imposing that the gas mass fraction
f_{gas} equals the cosmic value at the virial radius. Including such a
nonthermal component, we reconstruct from X rays an increasing mass profile
consistent with the hydrostatic equilibrium also in the cluster outskirts and
in agreement at the virial boundary with the weak lensing value. The increasing
f_{gas} profile confirms that the baryons are not missing but located at the
cluster outskirts.
On the origin of the warm-hot absorbers in the Milky Way's halo. (arXiv:1305.2964v1 [astro-ph.GA])
On the origin of the warm-hot absorbers in the Milky Way's halo. (arXiv:1305.2964v1 [astro-ph.GA]):
Disc galaxies like the Milky Way are expected to be surrounded by massive
coronae of hot plasma that may contain a significant fraction of the so-called
missing baryons. We investigate whether the local (|vLSR|<400 km/s) warm-hot
absorption features observed towards extra-Galactic sources or halo stars are
consistent with being produced by the cooling of the Milky Way's corona. In our
scheme, cooling occurs at the interface between the disc and the corona and it
is triggered by positive supernova feedback. We combine hydrodynamical
simulations with a dynamical 3D model of the galactic fountain to predict the
all-sky distribution of this cooling material, and we compare it with the
observed distribution of detections for different `warm' (SiIII, SiIV, CII,
CIV) and `hot' (OVI) ionised species. The model reproduces the
position-velocity distribution and the column densities of the vast majority of
warm absorbers and about half of OVI absorbers. We conclude that the warm-hot
gas responsible for most of the detections lies within a few kiloparsecs from
the Galactic plane, where high-metallicity material from the disc mixes
efficiently with the hot corona. This process provides an accretion of a few
Mo/yr of fresh gas that can easily feed the star formation in the disc of the
Galaxy. The remaining OVI detections are likely to be a different population of
absorbers, located in the outskirts of the Galactic corona and/or in the
circumgalactic medium of nearby galaxies.
Disc galaxies like the Milky Way are expected to be surrounded by massive
coronae of hot plasma that may contain a significant fraction of the so-called
missing baryons. We investigate whether the local (|vLSR|<400 km/s) warm-hot
absorption features observed towards extra-Galactic sources or halo stars are
consistent with being produced by the cooling of the Milky Way's corona. In our
scheme, cooling occurs at the interface between the disc and the corona and it
is triggered by positive supernova feedback. We combine hydrodynamical
simulations with a dynamical 3D model of the galactic fountain to predict the
all-sky distribution of this cooling material, and we compare it with the
observed distribution of detections for different `warm' (SiIII, SiIV, CII,
CIV) and `hot' (OVI) ionised species. The model reproduces the
position-velocity distribution and the column densities of the vast majority of
warm absorbers and about half of OVI absorbers. We conclude that the warm-hot
gas responsible for most of the detections lies within a few kiloparsecs from
the Galactic plane, where high-metallicity material from the disc mixes
efficiently with the hot corona. This process provides an accretion of a few
Mo/yr of fresh gas that can easily feed the star formation in the disc of the
Galaxy. The remaining OVI detections are likely to be a different population of
absorbers, located in the outskirts of the Galactic corona and/or in the
circumgalactic medium of nearby galaxies.
Multi-resonance orbital model of high-frequency quasi-periodic oscillations: possible high-precision determination of black hole and neutron star spin. (arXiv:1305.3552v1 [astro-ph.HE])
Multi-resonance orbital model of high-frequency quasi-periodic oscillations: possible high-precision determination of black hole and neutron star spin. (arXiv:1305.3552v1 [astro-ph.HE]):
Using known frequencies of the twin-peak high-frequency quasiperiodic
oscillations (HF QPOs) and known mass of the central black hole, the black-hole
dimensionless spin can be determined by assuming a concrete version of the
resonance model. However, a wide range of observationally limited values of the
black hole mass implies low precision of the spin estimates. We discuss the
possibility of higher precision of the black hole spin measurements in the
framework of a multi-resonance model inspired by observations of more than two
HF QPOs in the black hole systems, which are expected to occur at two (or more)
different radii of the accretion disc. For the black hole systems we focus on
the special case of duplex frequencies, when the top, bottom, or mixed
frequency is common at two different radii where the resonances occur giving
triple frequency sets. The sets of triple frequency ratios and the related spin
are given. The strong resonance model for "magic" values of the black hole spin
means that two (or more) versions of resonance could occur at the same radius,
allowing cooperative effects between the resonances. For neutron star systems
we introduce a resonant switch model that assumes switching of oscillatory
modes at resonant points. In the case of doubled twin-peak HF QPOs excited at
two different radii with common top, bottom, or mixed frequency, the black hole
spin is given by the triple frequency ratio set. The spin is determined
precisely, but not uniquely, because the same frequency set could correspond to
more than one concrete spin. The black hole mass is given by the magnitude of
the observed frequencies. The resonant switch model puts relevant limits on the
mass and spin of neutron stars, and we expect a strong increase in the fitting
procedure precision when different twin oscillatory modes are applied to data
in the vicinity of different resonant points.
Using known frequencies of the twin-peak high-frequency quasiperiodic
oscillations (HF QPOs) and known mass of the central black hole, the black-hole
dimensionless spin can be determined by assuming a concrete version of the
resonance model. However, a wide range of observationally limited values of the
black hole mass implies low precision of the spin estimates. We discuss the
possibility of higher precision of the black hole spin measurements in the
framework of a multi-resonance model inspired by observations of more than two
HF QPOs in the black hole systems, which are expected to occur at two (or more)
different radii of the accretion disc. For the black hole systems we focus on
the special case of duplex frequencies, when the top, bottom, or mixed
frequency is common at two different radii where the resonances occur giving
triple frequency sets. The sets of triple frequency ratios and the related spin
are given. The strong resonance model for "magic" values of the black hole spin
means that two (or more) versions of resonance could occur at the same radius,
allowing cooperative effects between the resonances. For neutron star systems
we introduce a resonant switch model that assumes switching of oscillatory
modes at resonant points. In the case of doubled twin-peak HF QPOs excited at
two different radii with common top, bottom, or mixed frequency, the black hole
spin is given by the triple frequency ratio set. The spin is determined
precisely, but not uniquely, because the same frequency set could correspond to
more than one concrete spin. The black hole mass is given by the magnitude of
the observed frequencies. The resonant switch model puts relevant limits on the
mass and spin of neutron stars, and we expect a strong increase in the fitting
procedure precision when different twin oscillatory modes are applied to data
in the vicinity of different resonant points.
Zooming towards the Event Horizon - mm-VLBI today and tomorrow. (arXiv:1305.2811v1 [astro-ph.HE])
Zooming towards the Event Horizon - mm-VLBI today and tomorrow. (arXiv:1305.2811v1 [astro-ph.HE]):
Global VLBI imaging at millimeter and sub-millimeter wavelength overcomes the
opacity barrier of synchrotron self-absorption in AGN and opens the direct view
into sub-pc scale regions not accessible before. Since AGN variability is more
pronounced at short millimeter wavelength, mm-VLBI can reveal structural
changes in very early stages after outbursts. When combined with observations
at longer wavelength, global 3mm and 1mm VLBI adds very detailed information.
This helps to determine fundamental physical properties at the jet base, and in
the vicinity of super-massive black holes at the center of AGN. Here we present
new results from multi-frequency mm-VLBI imaging of OJ287 during a major
outburst. We also report on a successful 1.3mm VLBI experiment with the APEX
telescope in Chile. This observation sets a new record in angular resolution.
It also opens the path towards future mm-VLBI with ALMA, which aims at the
mapping of the black hole event horizon in nearby galaxies, and the study of
the roots of jets in AGN.
Global VLBI imaging at millimeter and sub-millimeter wavelength overcomes the
opacity barrier of synchrotron self-absorption in AGN and opens the direct view
into sub-pc scale regions not accessible before. Since AGN variability is more
pronounced at short millimeter wavelength, mm-VLBI can reveal structural
changes in very early stages after outbursts. When combined with observations
at longer wavelength, global 3mm and 1mm VLBI adds very detailed information.
This helps to determine fundamental physical properties at the jet base, and in
the vicinity of super-massive black holes at the center of AGN. Here we present
new results from multi-frequency mm-VLBI imaging of OJ287 during a major
outburst. We also report on a successful 1.3mm VLBI experiment with the APEX
telescope in Chile. This observation sets a new record in angular resolution.
It also opens the path towards future mm-VLBI with ALMA, which aims at the
mapping of the black hole event horizon in nearby galaxies, and the study of
the roots of jets in AGN.
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