5,810 research outputs found
The Spectral Evolution along the Z track of the Bright Neutron Star X-ray Binary GX 17+2
Z sources are bright neutron-star X-ray binaries, accreting at around the
Eddington limit. We analyze the 68 RXTE observations (270 ks) of Sco-like Z
source GX 17+2 made between 1999 October 3-12, covering a complete Z track. We
create and fit color-resolved spectra with a model consisting of a thermal
multicolor disk, a single-temperature-blackbody boundary layer and a weak
Comptonized component. We find that, similar to what was observed for XTE
J1701-462 in its Sco-like Z phase, the branches of GX 17+2 can be explained by
three processes operating at a constant accretion rate Mdot into the disk:
increase of Comptonization up the horizontal branch, transition from a standard
thin disk to a slim disk up the normal branch, and temporary fast decrease of
the inner disk radius up the flaring branch. We also model the Comptonization
in an empirically self-consistent way, with its seed photons tied to the
thermal disk component and corrected for to recover the pre-Comptonized thermal
disk emission. This allows us to show a constant Mdot along the entire Z track
based on the thermal disk component. We also measure the upper kHz QPO
frequency and find it to depend on the apparent inner disk radius R_in (prior
to Compton scattering) approximately as frequency \propto R_in^(-3/2),
supporting the idenfitication of it as the Keplerian frequency at R_in. The
horizontal branch oscillation is probably related to the dynamics in the inner
disk as well, as both its frequency and R_in vary significantly on the
horizontal branch but become relatively constant on the normal branch.Comment: 17 pages, 14 figures. Accepted for publication in Ap
First results from TOO observations of the Aql X-1 field with INTEGRAL
We present results of observations of the Aql X-1 field performed in
March-April 2003 with the INTEGRAL observatory. This TOO (Target Of
Opportunity) INTEGRAL observations was initiated upon receiving an indication
from the ASM/RXTE that the source started an outburst. Thirteen X-ray sources
were detected by the INTEGRAL imagers, JEM-X and IBIS, during these
observations. We present a preliminary spectral and timing analysis for several
bright sources in the field, Aql X-1, X1901+03, 4U1907+097, XTE J1908+094 and
X1908+075. We also detected two X-ray bursts from Aql X-1 near the end of the
general outburst episode.Comment: 5 pages, 7 figures, accepted for publication in the A&
A search for hyperluminous X-ray sources in the XMM-Newton source catalog
We present a new method to identify luminous off-nuclear X-ray sources in the
outskirts of galaxies from large public redshift surveys, distinguishing them
from foreground and background interlopers. Using the 3XMM-DR5 catalog of X-ray
sources and the SDSS DR12 spectroscopic sample of galaxies, with the help of
this off-nuclear cross-matching technique, we selected 98 sources with inferred
X-ray luminosities in the range , compatible with hyperluminous X-ray objects (HLX). To validate
the method, we verify that it allowed us to recover known HLX candidates such
as ESO 24349 HLX1 and M82 X1. From a statistical study, we
conservatively estimate that up to of these sources may be fore- or
background sources, statistically leaving at least 16 that are likely to be
HLXs, thus providing support for the existence of the HLX population. We
identify two good HLX candidates and using other publicly available datasets,
in particular the VLA FIRST in radio, UKIDSS in the near-infrared, GALEX in the
ultra-violet and CFHT Megacam archive in the optical, we present evidence that
these objects are unlikely to be foreground or background X-ray objects of
conventional types, e.g. active galactic nuclei, BL Lac objects, Galactic X-ray
binaries or nearby stars. However, additional dedicated X-ray and optical
observations are needed to confirm their association with the assumed host
galaxies and thus secure their HLX classification.Comment: 20 pages, 6 figures, accepted to Ap
X-ray sources and their optical counterparts in the globular cluster M 22
Using XMM-Newton EPIC imaging data, we have detected 50 low-luminosity X-ray
sources in the field of view of M 22, where 5 +/- 3 of these sources are likely
to be related to the cluster. Using differential optical photometry, we have
identified probable counterparts to those sources belonging to the cluster.
Using X-ray spectroscopic and timing studies, supported by the optical colours,
we propose that the most central X-ray sources in the cluster are cataclysmic
variables, millisecond pulsars, active binaries and a blue straggler. We also
identify a cluster of galaxies behind this globular cluster.Comment: 11 pages, 7 figures, accepted for publication in A&
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