130 research outputs found
X-ray Sources in Galactic Globular Clusters
I review recent work on X-ray sources in Galactic globular clusters,
identified with low-mass X-ray binaries (LMXBs), cataclysmic variables (CVs),
millisecond pulsars (MSPs) and coronally active binaries by Chandra. Faint
transient LMXBs have been identified in several clusters, challenging our
understanding of accretion disk instabilities. Spectral fitting of X-rays from
quiescent LMXBs offers the potential to constrain the interior structure of
neutron stars. The numbers of quiescent LMXBs scale with the dynamical
interaction rates of their host clusters, indicating their dynamical formation.
Large numbers of CVs have been discovered, including a very faint population in
NGC 6397 that may be at or beyond the CV period minimum. Most CVs in dense
clusters seem to be formed in dynamical interactions, but there is evidence
that some are primordial binaries. Radio millisecond pulsars show thermal
X-rays from their polar caps, and often nonthermal X-rays, either from
magnetospheric emission, or from a shock between the pulsar wind and material
still flowing from the companion. Chromospherically active binaries comprise
the largest number of X-ray sources in globular clusters, and their numbers
generally scale with cluster mass, but their numbers seem to be reduced in all
globular clusters compared to other old stellar populations.Comment: To appear in the proceedings of the conference "Binary Star
Evolution: Mass Loss, Accretion and Mergers" (ed. V. Kalogera and M. van der
Sluys, AIP Conf. Ser.), held in Mykonos, Greece, held in June 22-25, 2010. 9
pages, 4 color figures. Slightly altered (from conf. version) to mention the
new transient LMXB in Terzan
Constraints on physics of neutron stars from X-ray observations
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.Comment: Refereed proceedings of XQCD 2012 conference (August 2012), to be
published online in the IOP Journal of Physics: Conference Series. 10 pages,
8 figure
Chance coincidences between black hole low-mass X-ray binaries and supernova remnants
I argue that black hole low-mass X-ray binaries (BH LMXBs) are very unlikely
to be physically associated with supernova remnants (SNRs). The timescales of
BH LMXBs are so much longer than those of SNRs, that there is only a 0.2%
chance of any BH LMXB being identified within its natal SNR. However, the
probability of a BH LMXB being projected within a SNR is significant; I
estimate that 2 BH LMXBs should be projected within SNRs from our perspective.
I look more closely at the suggestion by Balakrishnan and collaborators of an
association between the BH X-ray binary Swift J1728.9-3613 and the SNR
G351.9-0.9, and show that this is most likely a chance coincidence.Comment: ApJ, in press. 5 pages, 1 figur
A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Centauri: a correlation between spider pulsar companion mass and X-ray luminosity
Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in
Galactic globular clusters (GCs). In this work, we investigate 18 MSPs newly
found in the GC Omega Centauri ( Cen) and search for their X-ray
counterparts using Chandra observations with a total exposure time of 290.9 ks.
We identify confident X-ray counterparts for 11 of the MSPs, with 9 of them
newly identified in this work based on their positions, spectral properties,
and X-ray colours. The X-ray spectra of 9 MSPs are well described by a neutron
star hydrogen atmosphere model, while 2 MSPs are well fitted by a power-law
model. The identified MSPs have X-ray luminosities ranging from
erg s to erg s.
Additionally, for population comparison purposes, we study the X-ray
counterpart to MSP E in the GC M71, and find its X-ray spectrum is well
described by blackbody-like models with a luminosity of erg
s. We investigate the empirical correlations between X-ray luminosities
and minimum companion masses, as well as mass functions, of spider pulsars.
Clear correlations are observed, with best-fit functions of and , respectively, with an
intrinsic scatter of of 0.3, where is the 0.510
keV X-ray luminosity, is the minimum companion mass, and MF
represents the mass function, in solar masses.Comment: 18 pages, 8 figures, 8 tables; accepted for publication in MNRA
The X-ray Properties of Five Galactic Supernova Remnants Detected by the Spitzer GLIMPSE Survey
(Abbreviated) We present a study of the X-ray properties of five Galactic
supernova remnants (SNRs) -- Kes 17 (G304.60.1), G311.50.3, G346.60.2,
CTB 37A (G348.50.1) and G348.50.0 -- that were detected in the infrared
by Reach et al. (2006) in an analysis of data from the Galactic Legacy Infrared
Mid-Plane Survey Extraordinaire (GLIMPSE) that was conducted by the Spitzer
Space Telescope. We present and analyze archival ASCA observations of Kes 17,
G311.50.3 and G346.60.2, archival XMM-Newton observations of Kes 17, CTB
37A and G348.50.0 and an archival Chandra observation of CTB 37A. All of the
SNRs are clearly detected in the X-ray possibly except for G348.50.0. Our
study reveals that the four detected SNRs all feature center-filled X-ray
morphologies and that the observed emission from these sources is thermal in
all cases. We argue that these SNRs should be classified as mixed-morphology
SNRs (MM SNRs): our study strengthens the correlation between MM SNRs and SNRs
interacting with molecular clouds and suggests that the origin of
mixed-morphology SNRs may be due to the interactions between these SNRs and
adjacent clouds. Our ASCA analysis of G311.50.3 reveals for the first time
X-ray emission from this SNR: the X-ray emission is center-filled within the
radio and infrared shells and thermal in nature ( 0.98 keV), thus
motivating its classification as an MM SNR. We find considerable spectral
variations in the properties associated with the plasmas of the other
X-ray-detected SNRs, such as a possible overabundance of magnesium in the
plasma of Kes 17. Finally, we also estimate such properties as electron density
, radiative age and swept-up mass for each of the
four X-ray-detected SNRs.Comment: 78 pages, 26 figures, Astronomical Journal, in pres
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