140 research outputs found
Broad-band spectral changes of the microquasars Cygnus X-1 and SWIFT J1753.5-0127
We report high-energy results obtained with INTEGRAL and Rossi-XTE on two
microquasars: the persistent high-mass system Cygnus X-1 and the transient
low-mass binary SWIFT J1753.5-0127. INTEGRAL observed Cygnus X-1 from 2002 to
2004: the spectral (5-1000 keV) properties of the source, seen at least in
three distinct spectral states, show disc and corona changes. In 2003 June, a
high-energy tail at several hundred keV in excess of the thermal Comptonization
model was observed, suggesting the presence of an additional non-thermal
component. At that time, we detected an unusual correlation between radio data
and high-energy hardness. We also report and compare the results obtained with
simultaneous observations of the transient source SWIFT J1753.5-0127 performed
with Rossi-XTE, INTEGRAL, VLA, REM and NTT on 2005 August 10-12 near its hard
X-ray outburst. Broad-band spectra and fast time-variability properties are
derived on this source (probably located in the galactic halo) together with
radio, IR and optical data. We build a spectral energy distribution of the
source and derive interesting multiwavelength constraints. Significantly
detected up to 600 keV in a typical Low/Hard State, the transient does not seem
to follow the usual radio/X-ray correlation.Comment: 5 figures, 2 in colo
Polarized Gamma-ray Emission from the Galactic Black Hole Cygnus X-1
Because of their inherently high flux allowing the detection of clear
signals, black hole X-ray binaries are interesting candidates for polarization
studies, even if no polarization signals have been observed from them before.
Such measurements would provide further detailed insight into these sources'
emission mechanisms. We measured the polarization of the gamma-ray emission
from the black hole binary system Cygnus X-1 with the INTEGRAL/IBIS telescope.
Spectral modeling of the data reveals two emission mechanisms: The 250-400 keV
data are consistent with emission dominated by Compton scattering on thermal
electrons and are weakly polarized. The second spectral component seen in the
400keV-2MeV band is by contrast strongly polarized, revealing that the MeV
emission is probably related to the jet first detected in the radio band.Comment: 11 pages, 3 figures, to be published in Science in April 22nd 2011,
available on Science Express Web site (March 24th edition
Spectral state dependence of the 0.4-2 MeV polarized emission in Cygnus X-1 seen with INTEGRAL/IBIS, and links with the AMI radio data
Polarization of the >~400 keV hard tail of the microquasar Cygnus X-1 has
been independently reported by INTEGRAL/IBIS, and INTEGRAL/SPI and interpreted
as emission from a compact jet. These conclusions were, however, based on the
accumulation of all INTEGRAL data regardless of the spectral state. We utilize
additional INTEGRAL exposure accumulated until December 2012, and include the
AMI/Ryle (15 GHz) radio data in our study. We separate the observations into
hard, soft, and intermediate/transitional states and detect radio emission from
a compact jet in hard and intermediate states, but not in the soft. The 10-400
keV INTEGRAL (JEM-X and IBIS) state resolved spectra are well modeled with
thermal Comptonization and reflection components. We detect a hard tail in the
0.4-2 MeV range for the hard state only. We extract the state dependent
polarigrams of Cyg X-1, which all are compatible to no or undetectable level of
polarization except in 400-2000 keV range in the hard state where the
polarization fraction is 7532 % and the polarization angle 40.0 +-14 deg.
An upper limit on the 0.4-2 MeV soft state polarization fraction is 70%. Due to
the short exposure, we obtain no meaningful constraint for the intermediate
state. The likely detection of a >400 keV polarized tail in the hard state,
together with the simultaneous presence of a radio jet, reinforce the notion of
a compact jet origin of the 400 keV emission.Comment: 13 pages, 5 figures, accepted for publication in Ap
Detailed Radio to Soft Gamma-ray Studies of the 2005 Outburst of the New X-ray Transient XTE J1818-245
XTE J1818-245 is an X-ray nova that experienced an outburst in 2005, first
seen by the RXTE satellite. The source was observed simultaneously at various
wavelengths up to soft gamma-rays with the INTEGRAL satellite, from 2005
February to September. X-ray novae are extreme systems that often harbor a
black hole, and are known to emit throughout the electromagnetic spectrum when
in outburst. We analyzed radio, (N)IR, optical, X-ray and soft gamma-ray
observations and constructed simultaneous broad-band X-ray spectra. Analyzing
both the light curves in various energy ranges and the hardness-intensity
diagram enabled us to study the long-term behavior of the source. Spectral
parameters were typical of the Soft Intermediate States and the High Soft
States of a black hole candidate. The source showed relatively small spectral
variations in X-rays with considerable flux variation in radio. Spectral
studies showed that the accretion disc cooled down from 0.64 to 0.27 keV in 100
days and that the total flux decreased while the relative flux of the hot
medium increased. Radio emission was detected several times, and,
interestingly, five days after entering the HSS. Modeling the spectral energy
distribution from the radio to the soft gamma-rays reveals that the radio
flares arise from several ejection events. XTE J1818-245 is likely a black hole
candidate transient source that might be closer than the Galactic Bulge. The
results from the data analysis trace the physical changes that took place in
the system at a maximum bolometric luminosity of (0.4-0.9)e38 erg/s (assuming a
distance between 2.8-4.3 kpc) and they are discussed within the context of disc
and jet models.Comment: Accepted for publication in Astronomy and Astrophysics. 11 Figures, 3
Table
Spinning-Up: The Case of the Symbiotic X-Ray Binary 3A 1954+319
We present a timing and spectral analysis of the variable X-ray source 3A 1954+319, Our analysis is mainly based on an outburst serendipitously observed during INTEGRAL Key Program observations of the Cygnus region in 2008 fall and on the Swift/BAT longterm light curve, Previous observations, though sparse, have identified the source to be one of only nine known symbiotic X-ray binaries, i.e., systems composed of an accreting neutron star orbiting in a highly inhomogeneous medium around an M-giant companion. The spectrum of 3A 1954+319 above 20 keY can be best described by a broken power law model. The extremely long pulse period of approx.5.3 hours is clearly visible in the INTEGRAL/ISGRI light curve and confirmed through an epoch folding period search. Furthermore, the light curve allows us to determine a very strong spin up of -2x10(exp 4)h/h during the outburst. This spin up is confirmed by the pulse period evolution calculated from Swift/BAT data. The Swift/BAT data also show a long spin-down trend prior to the 2008 outburst. which is confirmed in archival INTEGRAL/ISGRI data. We discuss possible accretion models and geometries allowing for the transfer of such large amounts of angular momentum and investigate the harder spectrum of this outburst compared to previously published results
First simultaneous multi-wavelength observations of the black hole candidate IGR J17091-3624: ATCA, INTEGRAL, Swift, and RXTE views of the 2011 outburst
We present the results of the first four (quasi-)simultaneous radio (ATCA),
X-ray (Swift, RXTE), and Gamma-ray (INTEGRAL) observations of the black hole
candidate IGR J17091-3624, performed in February and March 2011. The X-ray
analysis shows that the source was in the hard state, and then it transited to
a soft intermediate state. We study the correlated radio/X-ray behaviour of
this source for the first time. The radio counterpart to IGR J17091-3624 was
detected during all four observations with the ATCA. In the hard state, the
radio spectrum is typical of optically thick synchrotron emission from a
self-absorbed compact jet. In the soft intermediate state, the detection of
optically thin synchrotron emission is probably due to a discrete ejection
event associated with the state transition. The position of IGR J17091-3624 in
the radio versus X-ray luminosity diagram (aka fundamental plane) is compatible
with that of the other black hole sources for distances greater than 11 kpc.
IGR J17091-3624 also appears as a new member of the few sources that show a
strong quenching of radio emission after the state transition. Using the
estimated luminosity at the spectral transition from the hard state, and for a
typical mass of 10 M_sun, we estimate a distance to the source between ~11 and
~17 kpc, compatible with the radio behaviour of the source.Comment: 6 pages, 4 figures, 1 online table, accepted for publication in A&
Simultaneous multiwavelength observations of the Low/Hard State of the X-ray transient source SWIFT J1753.5-0127
We report the results of simultaneous multiwavelength observations of the
X-ray transient source SWIFT J1753.5-0127 performed with INTEGRAL, RXTE, NTT,
REM and VLA on 2005 August 10-12. The source, which underwent an X-ray outburst
since 2005 May 30, was observed during the INTEGRAL Target of Opportunity
program dedicated to new X-ray novae located in the Galactic Halo. Broad-band
spectra and fast timing variability properties of SWIFT J1753.5-0127 are
analyzed together with the optical, near infra-red and radio data. We show that
the source was significantly detected up to 600 keV with Comptonization
parameters and timing properties typical of the so-called Low/Hard State of
black hole candidates. We build a spectral energy distribution and we show that
SWIFT J1753.5-0127 does not follow the usual radio/X-ray correlation of X-ray
binaries in the Low/Hard State. We give estimates of distance and mass. We
conclude that SWIFT J1753.5-0127 belongs to the X-ray nova class and that it is
likely a black hole candidate transient source of the Galactic Halo which
remained in the Low/Hard State during its main outburst. We discuss our results
within the context of Comptonization and jet models.Comment: Accepted for publication in ApJ, 25 pages, 4 tables, 11 figures (3 in
color
Overview of an Extensive Multi-wavelength Study of GX 339-4 during the 2010 Outburst
The microquasar GX 339-4 experienced a new outburst in 2010: it was observed
simultaneously at various wavelengths from radio up to soft gamma-rays. We
focused on observations that are quasi-simultaneous with those made with the
INTEGRAL and RXTE satellites: these were collected in 2010 March-April during
our INTEGRAL Target of Opportunity program, and during some of the other
INTEGRAL observing programs with GX 339-4 in the field-of-view. X-ray
transients are extreme systems that often harbour a black hole, and are known
to emit throughout the whole electromagnetic spectrum when in outburst. The
goals of our program are to understand the evolution of the physical processes
close to the black hole and to study the connections between the accretion and
ejection. We analysed radio, NIR, optical, UV, X-ray and soft gamma-ray
observations. We studied the source evolution in detail by producing light
curves, hardness-intensity diagrams and spectra. We fitted the broadband data
with phenomenological, then physical, models to study the emission coming from
the distinct components. Based on the energy spectra, the source evolved from
the canonical hard state to the canonical soft state. The source showed X-ray
spectral variations that were correlated with changes in radio, NIR and optical
emission. The bolometric flux increased from 0.8 to 2.9*10^{-8} erg cm^{-2}
s^{-1} while the relative flux and contribution of the hot medium globally
decreased. Reprocessing in the disc was likely to be strong at the end of our
observations. The source showed a behaviour similar to that of previous
outbursts, with some small deviations in the hard X-rays parameters' evolution.
The radio, NIR and optical emission from jets was detected, and seen to fade as
the source softened. The results are discussed within the context of disc and
jet models.Comment: 13 pages, 10 figures, 4 tables. Accepted by A&
Timing Analysis with INTEGRAL: Comparing Different Reconstruction Algorithms
INTEGRAL is one of the few instruments capable of detecting X-rays above 20keV. It is therefore in principle well suited for studying X-ray variability in this regime. Because INTEGRAL uses coded mask instruments for imaging, the reconstruction of light curves of X-ray sources is highly non-trivial. We present results from the comparison of two commonly employed algorithms, which primarily measure flux from mask deconvolution (ii-lc-extract) and from calculating the pixel illuminated fraction (ii-light). Both methods agree well for timescales above about 10 s, the highest time resolution for which image reconstruction is possible. For higher time resolution, ii-light produces meaningful results, although the overall variance of the lightcurves is not preserved
- …