Determining neutron star masses and radii using energy-resolved waveforms of X-ray burst oscillations. (arXiv:1304.2330v1 [astro-ph.HE])

Determining neutron star masses and radii using energy-resolved waveforms of X-ray burst oscillations. (arXiv:1304.2330v1 [astro-ph.HE]):
Simultaneous, precise measurements of the mass $M$ and radius $R$ of neutron
stars can yield uniquely valuable information about the still uncertain
properties of cold matter at several times the density of nuclear matter. One
method that could be used to measure $M$ and $R$ is to analyze the
energy-dependent waveforms of the X-ray flux oscillations seen during some
thermonuclear bursts from some neutron stars. These oscillations are thought to
be produced by X-ray emission from hotter regions on the surface of the star
that are rotating at or near the spin frequency of the star. Here we explore
how well $M$ and $R$ could be determined by generating, and analyzing using
Bayesian techniques, synthetic energy-resolved X-ray data that we produce
assuming a future space mission having 2--30 keV energy coverage and an
effective area of 10 m$^2$, such as the proposed \textit{LOFT} or
\textit{AXTAR} missions.

We find that if the hot spot is within 10$^\circ$ of the rotation equator,
both $M$ and $R$ can usually be determined with an uncertainty of about 10% if
there are $10^6$ total counts from the spot, whereas waveforms from spots
within 20$^\circ$ of the rotation pole provide no useful constraints. These
constraints can usually be achieved even if the burst oscillations vary with
time and data from multiple bursts must be used to obtain 10$^6$ counts from
the hot spot. This is therefore a promising method to constrain $M$ and $R$
tightly enough to discriminate strongly between competing models of cold,
high-density matter.

Powering of cool filaments in cluster cores by buoyant bubbles. I. Qualitative model. (arXiv:1304.3168v1 [astro-ph.HE])

Powering of cool filaments in cluster cores by buoyant bubbles. I. Qualitative model. (arXiv:1304.3168v1 [astro-ph.HE]):
Cool-core clusters (e.g., Perseus or M87) often possess a network of bright
gaseous filaments, observed in radio, IR, optical and X-ray bands. We propose
that these filaments are powered by the reconnection of the magnetic field in
the wakes of buoyant bubbles. AGN-inflated bubbles of relativistic plasma rise
buoyantly in the cluster atmosphere, stretching and amplifying the field in the
wake to values of $\beta =8\pi P_{gas}/B^2\sim 1$. The field lines in the wake
have opposite directions and are forced together as the bubble motion stretches
the filament. This setup bears strong similarity to the coronal loops on the
Sun or the Earth magneto-tail. The reconnection process naturally explains both
the required level of local dissipation rate in filaments and the overall
luminosity of filaments. The original source of power for the filaments is the
potential energy of buoyant bubbles, inflated by the central AGN.

The Crab Nebula and the class of Type IIn-P supernovae caused by sub-energetic electron capture explosions. (arXiv:1304.0689v1 [astro-ph.HE])

The Crab Nebula and the class of Type IIn-P supernovae caused by sub-energetic electron capture explosions. (arXiv:1304.0689v1 [astro-ph.HE]):
What sort of supernova gave rise to the Crab Nebula? There are several
indications that the Crab arose from a sub-energetic explosion of an 8-10 Msun
star, this appears to conflict with the high luminosity indicated by historical
observations. This paper shows that several properties of the Crab are best
suited to Type IIn-P explosions (Type IIn spectra with plateau light curves).
These events probably arise from relatively low-energy (1e50 erg) explosions
with low 56Ni yield resulting from electron-capture SNe (ecSNe), but their high
luminosity and Type IIn spectra are dominated by shock interaction with CSM.
After about 120 days, nearly all of the mass in the CSM and ejecta ends up in a
slow dense shell. In the scenario proposed here for SN1054, this thin shell is
accelerated by the growing pulsar wind nebula, producing the complex network of
filaments seen today. There is no need to invoke the invisible fast SN envelope
hypothesized to reside outside the Crab. SNeIIn-P explain several observed
features of the Crab: (1) No blast wave or rapidly expanding SN envelope
outside the filaments, (2) a total mass of 5 Msun swept up in a thin shell, (3)
a high peak luminosity despite the low kinetic energy, and (4) chemical
abundances consistent with an 8-10 Msun star and low 56Ni yield. A number of
other implications are discussed, concerning other plerionic remnants, dust in
the Crab filaments, diversity in the initial masses of SNe IIn, and an
association between ecSNe and SN impostors. This model predicts that if light
echoes from SN1054 are discovered, they will be consistent with a Type IIn-P
spectrum.

AGN feedback in clusters: shock and sound heating. (arXiv:1304.0400v1 [astro-ph.CO])

AGN feedback in clusters: shock and sound heating. (arXiv:1304.0400v1 [astro-ph.CO]):
Observations support the view that feedback, in the form of radio outbursts
from active nuclei in central galaxies, prevents catastrophic cooling of gas
and rapid star formation in many groups and clusters of galaxies. Variations in
jet power drive a succession of weak shocks that can heat regions close to the
active galactic nuclei (AGN). On larger scales, shocks fade into sound waves.
The Braginskii viscosity determines a well-defined sound damping rate in the
weakly magnetized intracluster medium (ICM) that can provide sufficient heating
on larger scales. It is argued that weak shocks and sound dissipation are the
main means by which radio AGN heat the ICM, in which case, the power spectrum
of AGN outbursts plays a central role in AGN feedback.

Stellar Coronae, Solar Flares: a Detailed Comparison of sigma Gem, HR 1099, and the Sun in High-resolution X-rays. (arXiv:1304.0408v1 [astro-ph.SR])

Stellar Coronae, Solar Flares: a Detailed Comparison of sigma Gem, HR 1099, and the Sun in High-resolution X-rays. (arXiv:1304.0408v1 [astro-ph.SR]):
Chandra HETG spectra of the coronally active binary stars sigma Gem and HR
1099 are among the highest fluence observations for such systems taken at high
spectral resolution in x-rays with this instrument. We compare their properties
to solar flare spectra obtained with the Russian CORONAS-F RESIK instrument at
similar resolution in an overlapping bandpass. We emphasize the comparisons of
the 3.3-6.1 A region from solar flare spectra to the corresponding sigma Gem
and HR 1099 spectra. We also model the the HETG spectra from 1.7-25 A to
determine coronal temperatures and elemental abundances. Sigma Gem is a single
lined coronally active long period binary which has a very hot corona. HR 1099
is a similar, but shorter period, double lined system. In the deep exposures we
study emission from some of the weaker species, such as K, Na, and Al, which
have the lowest first ionization potentials (FIP). The solar flare temperatures
reach ~20 MK, comparable to the sigma Gem and HR 1099 coronae. During the
Chandra exposures, sigma Gem was slowly decaying from a flare and its spectrum
is well characterized by a collisional ionization equilibrium plasma with a
broad temperature distribution ranging from 2-60 MK, peaking near 25 MK, but
with substantial emission from 50 MK plasma. We have detected K XVIII and Na XI
emission which allow us to set limits on their abundances. HR 1099 was also in
a flare state but had no detectable K XVIII. These measurements provide new
comparisons of solar and stellar coronal abundances, especially at the lowest
FIP values. The low FIP elements do not show enhancement in the stellar coronae
as they do in the Sun, except for K in sigma Gem. Sigma Gem and HR 1099 differ
in their emission measure distributions but have very similar elemental
abundances.

Collisionless shocks in partly ionized plasma with cosmic rays: microphysics of non-thermal components. (arXiv:1304.0998v1 [astro-ph.HE])

Collisionless shocks in partly ionized plasma with cosmic rays: microphysics of non-thermal components. (arXiv:1304.0998v1 [astro-ph.HE]):
In this review we discuss some observational aspects and theoretical models
of astrophysical collisionless shocks in partly ionized plasma with the
presence of non-thermal components. A specific feature of fast strong
collisionless shocks is their ability to accelerate energetic particles that
can modify the shock upstream flow and form the shock precursors. We discuss
the effects of energetic particle acceleration and associated magnetic field
amplification and decay in the extended shock precursors on the line and
continuum multi-wavelength emission spectra of the shocks. Both Balmer-type and
radiative astrophysical shocks are discussed in connection to supernova
remnants interacting with partially neutral clouds. Quantitative models
described in the review predict a number of observable line-like emission
features that can be used to reveal the physical state of the matter in the
shock precursors and the character of nonthermal processes in the shocks.
Implications of recent progress of gamma-ray observations of supernova remnants
in molecular clouds are highlighted.

Proton-rich nucleosynthesis and nuclear physics. (arXiv:1304.0929v1 [astro-ph.SR])

Proton-rich nucleosynthesis and nuclear physics. (arXiv:1304.0929v1 [astro-ph.SR]):
Although the detailed conditions for explosive nucleosynthesis are derived
from astrophysical modeling, nuclear physics determines fundamental patterns in
abundance yields, not only for equilibrium processes. Focussing on the nu-p-
and the gamma-process, general nucleosynthesis features within the range of
astrophysical models, but (mostly) independent of details in the modelling, are
presented. Remaining uncertainties due to uncertain Q-values and reaction rates
are discussed.