Black Hole-Neutron Star Mergers with a Hot Nuclear Equation of State: Outflow and Neutrino-Cooled Disk for a Low-Mass, High-Spin Case. (arXiv:1304.3384v2 [astro-ph.HE] UPDATED)

via astro-ph updates on arXiv.org http://arxiv.org/abs/1304.3384

The origin of blue-shifted absorption features in the X-ray spectrum of PG 1211+143: Outflow or disc?. (arXiv:1306.3404v1 [astro-ph.HE])

The origin of blue-shifted absorption features in the X-ray spectrum of PG 1211+143: Outflow or disc?. (arXiv:1306.3404v1 [astro-ph.HE]):
In some radio-quiet active galaxies (AGN), high-energy absorption features in
the x-ray spectra have been interpreted as Ultrafast Outflows (UFOs) -- highly
ionised material (e.g. Fe XXV and Fe XXVI) ejected at mildly relativistic
velocities. In some cases, these outflows can carry energy in excess of the
binding energy of the host galaxy. Needless to say, these features demand our
attention as they are strong signatures of AGN feedback and will influence
galaxy evolution. For the same reason, alternative models need to be discussed
and refuted or confirmed. Gallo & Fabian proposed that some of these features
could arise from resonance absorption of the reflected spectrum in a layer of
ionised material located above and corotating with the accretion disc.
Therefore, the absorbing medium would be subjected to similar blurring effects
as seen in the disc. A priori, the existence of such plasma above the disc is
as plausible as a fast wind. In this work, we highlight the ambiguity by
demonstrating that the absorption model can describe the ~7.6 keV absorption
feature (and possibly other features) in the quasar PG 1211+143, an AGN that is
often described as a classic example of an UFO. In this model, the 2-10 keV
spectrum would be largely reflection dominated (as opposed to power law
dominated in the wind models) and the resonance absorption would be originating
in a layer between about 6 and 60 gravitational radii. The studies of such
features constitutes a cornerstone for future X-ray observatories like Astro-H
and Athena+. Should our model prove correct, or at least important in some
cases, then absorption will provide another diagnostic tool with which to probe
the inner accretion flow with future missions.

On the Statistical Analysis of X-ray Polarization Measurements. (arXiv:1306.3885v1 [astro-ph.IM])

On the Statistical Analysis of X-ray Polarization Measurements. (arXiv:1306.3885v1 [astro-ph.IM]):
In many polarimetry applications, including observations in the X-ray band,
the measurement of a polarization signal can be reduced to the detection and
quantification of a deviation from uniformity of a distribution of measured
angles. We explore the statistics of such polarization measurements using Monte
Carlo simulations and chi-squared fitting methods. We compare our results to
those derived using the traditional probability density used to characterize
polarization measurements and quantify how they deviate as the intrinsic
modulation amplitude grows. We derive relations for the number of counts
required to reach a given detection level (parameterized by beta, the "number
of sigma's" of the measurement) appropriate for measuring the modulation
amplitude by itself (single interesting parameter case) or jointly with the
position angle (two interesting parameters case). We show that for the former
case when the intrinsic amplitude is equal to the well known minimum detectable
polarization (MDP) it is, on average, detected at the 3-sigma level. For the
latter case, when one requires a joint measurement at the same confidence
level, then more counts are needed than that required to achieve the MDP level.
This additional factor is amplitude-dependent, but is approximately 2.2 for
intrinsic amplitudes less than about 20%. It decreases slowly with amplitude
and is 1.8 when the amplitude is 50%. We find that the position angle
uncertainty at 1-sigma confidence is well described by the relation 28.5 (deg)
/ beta.

GRB 130606A as a Probe of the Intergalactic Medium and the Interstellar Medium in a Star-forming Galaxy in the First Gyr After the Big Bang. (arXiv:1306.3949v1 [astro-ph.CO])

GRB 130606A as a Probe of the Intergalactic Medium and the Interstellar Medium in a Star-forming Galaxy in the First Gyr After the Big Bang. (arXiv:1306.3949v1 [astro-ph.CO]):
We present high signal-to-noise ratio Gemini and MMT spectroscopy of the
optical afterglow of the gamma-ray burst (GRB) 130606A at redshift z=5.913,
discovered by Swift. This is the first high-redshift GRB afterglow to have
spectra of comparable quality to those of z~6 quasars. The data exhibit a
smooth continuum at near-infrared wavelengths that is sharply cut off blueward
of 8410 Angs due to absorption from Ly-alpha at redshift z~5.91, with some flux
transmitted through the Ly-alpha forest between 7000-7800 Angs. We use column
densities inferred from metal absorption lines to constrain the metallicity of
the host galaxy between a lower limit of [Si/H]>-1.7 and an upper limit of
[S/H]<-0.5 set by the non-detection of S II absorption. We demonstrate
consistency between the dramatic evolution in the transmission fraction of
Ly-alpha seen in this spectrum over the redshift range z=4.9 to 5.85 with that
previously measured from observations of high-redshift quasars. There is an
extended redshift interval of Delta-z=0.12 in the Ly-alpha forest at z=5.77
with no detected transmission, leading to a 3-sigma upper limit on the mean
Ly-alpha transmission fraction of <0.2% (or tau_eff(Ly-alpha) > 6.4). This is
comparable to the lowest-redshift Gunn-Peterson troughs found in quasar
spectra. Some Ly-beta and Ly-gamma transmission is detected in this redshift
window, indicating that it is not completely opaque, and hence that the IGM is
nonetheless mostly ionized at these redshifts. GRB 130606A thus for the first
time realizes the promise of GRBs as probes of the first galaxies and cosmic
reionization.

CXOU J005047.9-731817: a 292-s X-ray binary pulsar in the Small Magellanic Cloud. (arXiv:1306.1106v1 [astro-ph.HE])

CXOU J005047.9-731817: a 292-s X-ray binary pulsar in the Small Magellanic Cloud. (arXiv:1306.1106v1 [astro-ph.HE]):
We report on the discovery of a transient X-ray pulsars, located in the Small
Magellanic Cloud, with a pulse period of 292 s. A series of Chandra pointings
fortuitously recorded in 2010 April-May the occurrence of a two-weeks-long
outburst, during which the source luminosity increased by a factor of about
100, reaching a peak of ~1E36 erg/s (for a distance of 61 kpc). Complex-shape
and energy-dependent pulsations were detected close to the outburst peak and
during the very first part of its decay phase. During the outburst, the
phase-averaged spectrum of the pulsar was well described by an absorbed power
law with photon index ~0.6, but large variations as a function of phase were
present. The source was also detected by Chandra several times (during 2002,
2003, 2006, and 2010) at a quiescent level of ~1E34 erg/s. In 2012 we performed
an infrared photometric follow-up of the R ~ 15 mag optical counterpart with
the ESO/VLT and a spectroscopic observation by means of the CTIO telescope. The
optical spectra suggest a late-Oe or early-Be V-III luminosity-class star,
though a more evolved companion cannot be ruled out by our data (we can exclude
a luminosity class I and a spectral type later than B2). Finally, we show that
the outburst main parameters (duration and peak luminosity) can be accounted
for by interpreting the source transient activity as a type I outburst in a Be
X-ray binary.

What can the spatial distribution of galaxy clusters tell about their scaling relations?. (arXiv:1306.1399v1 [astro-ph.CO])

What can the spatial distribution of galaxy clusters tell about their scaling relations?. (arXiv:1306.1399v1 [astro-ph.CO]):
We aim to quantify the capability of the inhomogeneous distribution of galaxy
clusters, represented by the two-point statistics in Fourier space, to retrieve
information on the underlying scaling relations. As an example, we use the
mass-X ray luminosity of galaxy clusters. We define the luminosity-weighted
power spectrum and introduce the luminosity power spectrum as a direct
assessment of the clustering of X-ray luminosity. Using a suite of halo
catalogs extracted from $N$-body simulations and realistic estimates of the
mass-X ray luminosity relation, we measure the luminosity-weighted and the
luminosity power spectrum of galaxy clusters. By means of a Fisher matrix
analysis, we quantify the content of information (by means of a Figure-of
Merit) encoded in the amplitude, shape and full-shape of these probes. The full
shape of the luminosity power spectrum, when analyzed up to scales of $k~0.2 h/
Mpc$, yields a figure of merit which is only one order of magnitude below the
value encoded in X-ray luminosity function estimated from the same sample. This
is a significant improvement with respect to the FoM obtained from the
estimates of the unweighted power spectrum. We therefore suggest future
clustering analysis of galaxy clusters to take advantage of the luminosity
power spectrum when aiming at simultaneously constraining cosmological and
astrophysical parameters (Abridged)

Constraints on porosity and mass loss in O-star winds from modeling of X-ray emission line profile shapes. (arXiv:1305.5595v1 [astro-ph.SR])

Constraints on porosity and mass loss in O-star winds from modeling of X-ray emission line profile shapes. (arXiv:1305.5595v1 [astro-ph.SR]):
We fit X-ray emission line profiles in high resolution XMM-Newton and Chandra
grating spectra of the early O supergiant Zeta Pup with models that include the
effects of porosity in the stellar wind. We explore the effects of porosity due
to both spherical and flattened clumps. We find that porosity models with
flattened clumps oriented parallel to the photosphere provide poor fits to
observed line shapes. However, porosity models with isotropic clumps can
provide acceptable fits to observed line shapes, but only if the porosity
effect is moderate. We quantify the degeneracy between porosity effects from
isotropic clumps and the mass-loss rate inferred from the X-ray line shapes,
and we show that only modest increases in the mass-loss rate (<~ 40%) are
allowed if moderate porosity effects (h_infinity <~ R_*) are assumed to be
important. Large porosity lengths, and thus strong porosity effects, are ruled
out regardless of assumptions about clump shape. Thus, X-ray mass-loss rate
estimates are relatively insensitive to both optically thin and optically thick
clumping. This supports the use of X-ray spectroscopy as a mass-loss rate
calibration for bright, nearby O stars.