Unified description of dense matter in neutron stars and magnetars. (arXiv:1301.2438v1 [astro-ph.HE])

Unified description of dense matter in neutron stars and magnetars. (arXiv:1301.2438v1 [astro-ph.HE]):
We have recently developed a set of equations of state based on the nuclear
energy density functional theory providing a unified description of the
different regions constituting the interior of neutron stars and magnetars. The
nuclear functionals, which were constructed from generalized Skyrme effective
nucleon-nucleon interactions, yield not only an excellent fit to essentially
all experimental atomic mass data but were also constrained to reproduce the
neutron-matter equation of state as obtained from realistic many-body
calculations.

Early Thermal X-ray Emission from Long Gamma-ray Bursts and Their Circumstellar Environments. (arXiv:1301.2421v1 [astro-ph.HE])

Early Thermal X-ray Emission from Long Gamma-ray Bursts and Their Circumstellar Environments. (arXiv:1301.2421v1 [astro-ph.HE]):
We performed a series of hydrodynamical calculations of an ultra-relativistic
jet propagating through a massive star and the circumstellar matter to
investigate the interaction between the ejecta and the circumstellar matter. We
succeed in distinguishing two qualitatively different cases in which the ejecta
are shocked and adiabatically cool. To examine whether the cocoon expanding at
subrelativistic speeds emits any observable signal, we calculate expected
photospheric emission from the cocoon. It is found that the emission can
explain early thermal X-ray emission recently found in some long gamma-ray
bursts. The result implies that the difference of the circumstellar environment
of long gamma-ray bursts can be probed by observing their early thermal X-ray
emission.

A comparative analysis of virial black-hole mass estimates of moderate-luminosity active galactic nuclei using Subaru/FMOS. (arXiv:1301.2332v1 [astro-ph.CO])

A comparative analysis of virial black-hole mass estimates of moderate-luminosity active galactic nuclei using Subaru/FMOS. (arXiv:1301.2332v1 [astro-ph.CO]):
We present an analysis of broad emission lines observed in
moderate-luminosity active galactic nuclei (AGNs), typical of those found in
X-ray surveys of deep fields, with the aim to test the validity of single-epoch
virial black hole mass estimates. We have acquired near-infrared (NIR) spectra
of AGNs up to z ~ 1.8 in the COSMOS and Extended Chandra Deep Field-South
Survey, with the Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru
Telescope. These low-resolution NIR spectra provide a significant detection of
the broad Halpha line that has been shown to be a reliable probe of black hole
mass at low redshift. Our sample has existing optical spectroscopy which
provides a detection of MgII, a broad emission line typically used for black
hole mass estimation at z > 1. We carry out a spectral-line fitting procedure
using both Halpha and MgII to determine the virial velocity of gas in the broad
line region, the monochromatic continuum luminosity at 3000 A, and the total
Halpha line luminosity. With a sample of 43 AGNs spanning a range of two
decades in luminosity (i.e., L ~ 10^44-46 ergs/s), we find a tight correlation
between the continuum and line luminosity with a distribution characterized by
<log(L_3000/L_Halpha)> = 1.52 and a dispersion sigma = 0.16. There is also a
close one-to-one relationship between the FWHM of Halpha and of MgII up to
10000 km/s with a dispersion of 0.14 in the distribution of the logarithm of
their ratios. Both of these then lead to there being very good agreement
between Halpha- and MgII-based masses over a wide range in black hole mass
(i.e., M_BH ~ 10^7-9 M_sun). We do find a small offset in MgII-based masses,
relative to those based on Halpha, of +0.17 dex and a dispersion sigma = 0.32.
In general, these results demonstrate that local scaling relations, using MgII
or Halpha, are applicable for AGN at moderate luminosities and up to z ~ 2.

A Chandra X-ray study of the interacting binaries in the old open cluster NGC6791. (arXiv:1301.2331v1 [astro-ph.HE])

A Chandra X-ray study of the interacting binaries in the old open cluster NGC6791. (arXiv:1301.2331v1 [astro-ph.HE]):
We present the first X-ray study of NGC6791, one of the oldest open clusters
known (8 Gyr). Our Chandra observation is aimed at uncovering the population of
close interacting binaries down to Lx ~ 1e30 erg/s (0.3-7 keV). We detect 86
sources within 8 arcmin of the cluster center, including 59 inside the
half-mass radius. We identify twenty sources with proper-motion cluster
members, which are a mix of cataclysmic variables (CVs), active binaries (ABs),
and binaries containing sub-subgiants. With follow-up optical spectroscopy we
confirm the nature of one CV. We discover one new, X-ray variable candidate CV
with Balmer and HeII emission lines in its optical spectrum; this is the first
X-ray--selected CV confirmed in an open cluster. The number of CVs per unit
mass is consistent with the field, suggesting that the 3-4 CVs observed in
NGC6791 are primordial. We compare the X-ray properties of NGC6791 with those
of a few old open (NGC6819, M67) and globular clusters (47Tuc, NGC6397). It is
puzzling that the number of ABs brighter than 1e30 erg/s normalized by cluster
mass is lower in NGC6791 than in M67 by a factor ~3 to 7. CVs, ABs, and
sub-subgiants brighter than 1e30 erg/s are under-represented per unit mass in
the globular clusters compared to the oldest open clusters, and this accounts
for the lower total X-ray luminosity per unit mass of the former. This
indicates that the net effect of dynamical encounters may be the destruction of
even some of the hardest (i.e. X-ray--emitting) binaries.

Finite temperature effects on anisotropic pressure and equation of state of dense neutron matter in an ultrastrong magnetic field. (arXiv:1301.0544v1 [nucl-th])

Finite temperature effects on anisotropic pressure and equation of state of dense neutron matter in an ultrastrong magnetic field. (arXiv:1301.0544v1 [nucl-th]):
Spin polarized states in dense neutron matter with recently developed Skyrme
effective interaction (BSk20 parametrization) are considered in the magnetic
fields $H$ up to $10^{20}$ G at finite temperature. In a strong magnetic field,
the total pressure in neutron matter is anisotropic, and the difference between
the pressures parallel and perpendicular to the field direction becomes
significant at $H>H_{th}\sim10^{18}$ G. The longitudinal pressure decreases
with the magnetic field and vanishes in the critical field
$10^{18}<H_c\lesssim10^{19}$ G, resulting in the longitudinal instability of
neutron matter. With increasing the temperature, the threshold $H_{th}$ and
critical $H_c$ magnetic fields also increase. The appearance of the
longitudinal instability prevents the formation of a fully spin polarized state
in neutron matter and only the states with moderate spin polarization are
accessible. The anisotropic equation of state is determined at densities and
temperatures relevant for the interiors of magnetars. The entropy of strongly
magnetized neutron matter turns out to be larger than the entropy of the
nonpolarized matter. This is caused by some specific details in the dependence
of the entropy on the effective masses of neutrons with spin up and spin down
in a polarized state.

Testing the space-time geometry around black hole candidates with the available radio and X-ray data. (arXiv:1301.0361v1 [gr-qc])

Testing the space-time geometry around black hole candidates with the available radio and X-ray data. (arXiv:1301.0361v1 [gr-qc]):
Astrophysical black hole candidates are thought to be the Kerr black holes
predicted by General Relativity, but the actual nature of these objects has
still to be proven. The Kerr black hole hypothesis can be tested by observing
strong gravity features and check if they are in agreement with the predictions
of General Relativity. In particular, the study of the properties of the
electromagnetic radiation emitted by the gas of the accretion disk can provide
information on the geometry of the space-time around these objects and
constrain possible deviations from the Kerr background.

Bright broad-band afterglows of gravitational wave bursts from binary neutron star mergers as a probe of millisecond magnetars. (arXiv:1301.0439v1 [astro-ph.HE])

Bright broad-band afterglows of gravitational wave bursts from binary neutron star mergers as a probe of millisecond magnetars. (arXiv:1301.0439v1 [astro-ph.HE]):
If double neutron star mergers leave behind a massive magnetar rather than a
black hole, a bright early afterglow can follow the gravitational wave burst
(GWB) even if there is no short gamma-ray burst (SGRB) - GWB association or
there is an association but the SGRB does not beam towards earth(zhang 2012).
Besides directly dissipating the proto-magnetar wind, we here suggest that the
magnetar wind could push the ejecta launched during the merger process, and
under certain conditions, would reach a relativistic speed. Such a
magnetar-powered ejecta, when interacting with the ambient medium, would
develop a bright broad-band afterglow due to synchrotron radiation. We study
this physical scenario in detail, and present the predicted X-ray, optical and
radio light curves for a range of magnetar and ejecta parameters. We show that
the X-ray and optical lightcurves usually peak around the magnetar spindown
time scale (10^3-10^5s), reaching brightness readily detectable by wide-field
X-ray and optical telescopes, and remain detectable for an extended period. The
radio afterglow peaks later, but is much brighter than the case without a
magnetar energy injection. Therefore, such bright broad-band afterglows, if
detected and combined with GWBs in the future, would be a probe of massive
millisecond magnetars and stiff equation-of-state for nuclear matter.