1,584 research outputs found
Localizing INTEGRAL Sources with Chandra: X-Ray and Multi-Wavelength Identifications and Energy Spectra
We report on Chandra observations of 18 hard X-ray (>20 keV) sources
discovered with the INTEGRAL satellite near the Galactic plane. For 14 of the
INTEGRAL sources, we have uncovered one or two potential Chandra counterparts
per source. These provide soft X-ray (0.3-10 keV) spectra and sub-arcsecond
localizations, which we use to identify counterparts at other wavelengths,
providing information about the nature of each source. Despite the fact that
all of the sources are within 5 degrees of the plane, four of the IGR sources
are AGN (IGR J01545+6437, IGR J15391-5307, IGR J15415-5029, and IGR
J21565+5948) and four others are likely AGN (IGR J03103+5706, IGR J09189-4418,
IGR J16413-4046, and IGR J16560-4958) based on each of them having a strong IR
excess and/or extended optical or near-IR emission. We compare the X-ray and
near-IR fluxes of this group of sources to those of AGN selected by their 2-10
keV emission in previous studies and find that these IGR AGN are in the range
of typical values. There is evidence in favor of four of the sources being
Galactic (IGR J12489-6243, IGR J15293-5609, IGR J16173-5023, and IGR
J16206-5253), but only IGR J15293-5609 is confirmed as a Galactic source as it
has a unique Chandra counterpart and a parallax measurement from previous
optical observations that puts its distance at 1.56+/-0.12 kpc. The 0.3-10 keV
luminosity for this source is 1.4e32 erg/s, and its optical/IR spectral energy
distribution is well described by a blackbody with a temperature of 4200-7000 K
and a radius of 12.0-16.4 Rsun. These values suggest that IGR J15293-5609 is a
symbiotic binary with an early K-type giant and a white dwarf accretor. We also
obtained likely Chandra identifications for IGR J13402-6428 and IGR
J15368-5102, but follow-up observations are required to constrain their source
types.Comment: 17 pages, accepted by Ap
The Evolution of Accreting Black Holes in Outburst
Black hole binaries exhibit dramatic changes in their X-ray spectral and
timing properties over time, providing important clues about the physical
processes that occur in these systems. Black holes and black hole candidates
are prime targets for RXTE with observational goals including the study of
extreme gravitational fields and jet formation mechanisms. The great wealth of
data from RXTE has helped us to learn about these systems as well as raising
new questions about accreting black holes. RXTE observations have allowed us to
study a wide range of black hole science topics including the connection
between the accretion disk and jets, the geometry of the inner accretion flow,
and the physical changes that occur between spectral states. In this
presentation, I discuss significant results on these topics that have been
obtained for persistent and transient black holes over the past several years,
and I present results from our program of X-ray and radio observations during
the decays of black hole transient outbursts.Comment: 8 pages, to appear in the proceedings of "X-Ray Timing 2003: Rossi
and Beyond," eds. P. Kaaret, F.K. Lamb, & J.H. Swank (Melville, NY: American
Institute of Physics
XMM-Newton observations of five INTEGRAL sources located towards the Scutum Arm
Results are presented for XMM-Newton observations of five hard X-ray sources
discovered by INTEGRAL in the direction of the Scutum Arm. Each source received
more than 20 ks of effective exposure time. We provide refined X-ray positions
for all five targets enabling us to pinpoint the most likely counterpart in
optical/infrared archives. Spectral and timing information (much of which are
provided for the first time) allow us to give a firm classification for IGR
J18462-0223 and to offer tentative classifications for the others. For IGR
J18462-0223, we discovered a coherent pulsation period of 997+-1 s which we
attribute to the spin of a neutron star in a highly-obscured (nH = 2e23 /cm2)
high-mass X-ray binary (HMXB). This makes IGR J18462-0223 the seventh
supergiant fast X-ray transient (SFXT) candidate with a confirmed pulsation
period. IGR J18457+0244 is a highly-absorbed (nH = 8e23 /cm2) source in which
the possible detection of an iron line suggests an active galactic nucleus
(AGN) of type Sey-2 situated at z = 0.07(1). A periodic signal at 4.4 ks could
be a quasi-periodic oscillation which would make IGR J18457+0244 one of a
handful of AGN in which such features have been claimed, but a slowly-rotating
neutron star in an HMXB can not be ruled out. IGR J18482+0049 represents a new
obscured HMXB candidate with nH = 4e23 /cm2. We tentatively propose that IGR
J18532+0416 is either an AGN or a pulsar in an HMXB system. The X-ray spectral
properties of IGR J18538-0102 are consistent with the AGN classification that
has been proposed for this source.Comment: 15 pages, 9 figures, 4 tables: accepted for publication in Ap
The rise and fall of the compact jet in GRO J1655-40
In this work, we present some preliminary results on a multi-wavelength (radio/infrared/optical/X-ray) study of GRO J1655-40 during its 2005 outburst. We focus on the broadband spectral energy distribution during the different stages of the outburst. In particular, using this unprecedented coverage, and especially thanks to the new constraints given in the mid-IR by Spitzer, we can test the physical self-consistent disk-jet model during the hard state, where the source shows radio emission from a compact jet. The hard state broadband spectra of the observations during the decay of the outburst, are fairly well fit using the jet model with parameters overall similar to those found for Cyg X-1 and GX 339-4 in a previous work. However, we find that, compared to the other two BHs, GRO J1655-40 has a much higher jet power (at least a factor of 3), and that, most notably, the model seems to underestimate the radio emissio
Swift follow-up observations of 17 INTEGRAL sources of uncertain or unknown nature
(abridged) We analysed data from observations of 17 INTEGRAL sources made
with the Swift satellite. We refine the position of the hard X-ray sources to
an accuracy of a few arcsec. We then browsed the online catalogs (e.g., NED,
SIMBAD, 2MASS, 2MASX, USNO) to search for counterparts at other wavelengths. We
also made use of the X-ray spectral parameters to try to identify the nature of
those sources. We provide the X-ray position with arcsec accuracy, identify
possible infrared and optical counterparts (when found), give the magnitudes in
those bands and in the optical and UV as seen with the Swift/UVOT telescope
when observations are available. We confirm the previously suggested
associations and source types for IGR J03532-6829, J05346-5759, J10101-5654,
J13000+2529, J13020-6359, J15479-4529, J18214-1318, and J23206+6431. We
identify
IGR J09025-6814 as an AGN for the first time, and we suggest that it may be a
Seyfert 2. We suggest that IGR J05319-6601, J16287-5021, J17353-3539 and
J17476-2253 are X-ray binaries, with J05319-6601 being located in the LMC and
the other three possibly being HMXBs in our Galaxy. For IGR J15161-3827 and
J20286+2544, we find several possible X-ray counterparts in the IBIS error
region, and we discuss which, if any, are the likely counterparts. Both are
likely AGNs, although the latter could be a blend of two AGNs. For IGR
J03184-0014 and J19267+1325, we find X-ray sources slightly outside the IBIS
error circle. In the former, we do not favour an association of the Swift and
INTEGRAL source, while it is very likely that IGR J19267+1325 and the Swift
source are the same.Comment: 12 pages, 3 figures, accepted for publication in A&
Spectral evolution of the microquasar XTE J1550-564 over its entire 2000 outburst
We report on RXTE observations of the microquasar XTE J1550-564 during a ~70
day outburst in April-June 2000. We study the evolution of the PCA+HEXTE
spectra over the outburst. The source transited from an initial Low Hard State
(LS), to an Intermediate State (IS), and then back to the LS. The source shows
an hysteresis effect similar to what is observed in other sources, favoring a
common origin for the state transitions in soft X-ray transients. The first
transition occurs at a ~ constant 2-200 keV flux, which probably indicates a
change in the relative importance of the emitting media. The second transition
is more likely driven by a drop in the mass accretion rate.
In both LS, the spectra are characterized by the presence of a strong
power-law tail (Compton corona) with a variable high energy cut-off. During the
IS, the spectra show the presence of a ~0.8 keV thermal component (accretion
disk). We discuss the apparently independent evolution of the two media, and
show that right after the X-ray maximum on MJD 51662, the decrease of the
source luminosity is due to a decrease of the power-law luminosity, at a
constant disk luminosity. This, together with the detection of radio emission
(with a spectrum typical of optically thin synchrotron emission), may suggest
that the corona is ejected and further detected as a discrete radio ejection.Comment: Accepted for publication in ApJ. 9 pages, 4 figures, abstract
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