70 research outputs found
3-200 keV spectral states and variability of the INTEGRAL Black Hole binary IGR J17464-3213
On March 2003, IBIS, the gamma-ray imager on board the INTEGRAL satellite,
detected an outburst from a new source, IGR J17464-3213, that turned out to be
a HEAO-1 transient, H1743-322. In this paper we report on the high energy
behaviour of this BHC studied with the three main instruments onboard INTEGRAL.
The data, collected with unprecedented sensitivity in the hard X-Ray range,
show a quite hard Comptonised emission from 3 keV up to 150 keV during the
rising part of the source outburst, with no thermal emission detectable. A few
days later, a prominent soft disk multicolour component appears, with the hard
tail luminosity almost unchanged: 10-9 erg*cm-2*s-1. Two months later, during a
second monitoring campaign near the end of the outburst, the observed disk
component was unchanged. Conversely, the Comptonised emission from the
central-hot part of the disk reduced by a factor of 10. We present here its
long term behaviour in different energy ranges and the combined JEM-X, SPI and
IBIS wide band spectral evolution of this source.Comment: 12 pages, 4 figures, accepted for pubblication in AP
Hard X-ray emission of the microquasar GX 339-4 in the low/hard state
We present the analysis of the high-energy emission of the Galactic black hole binary GX 339-4 in a low/hard state at the beginning of its 2004 outburst. The data from 273 ks of INTEGRAL observations, spread over 4 weeks, are analyzed, along with the existing simultaneous RXTE HEXTE and PCA data. During this period, the flux increases by a factor of ~=3, while the spectral shape is quite unchanged, at least up to 150 keV. The high-energy data allow us to detect the presence of a high-energy cutoff, generally related to thermal mechanisms, and to estimate the plasma parameters in the framework of the Comptonization models. We found an electron temperature of 60-70 keV and an optical depth of around 2.5, with a rather low reflection factor (0.2-0.4). In the last observation, we detected a high-energy excess above 200 keV with respect to thermal Comptonization, while at lower energies the spectrum is practically identical to the previous one taken just 2 days before. This suggests that the low- and high-energy components have a different origin
Hard X-ray emission of the microquasar GRO J1655-40 during the rise of its 2005 outburst
We present the analysis of the high energy emission of the Galactic black
hole GRO J1655-40 at the beginning of its 2005 outburst. The data from 458 ks
of INTEGRAL observations, spread over 4 weeks, are analyzed, along with the
existing simultaneous RXTE and Swift data. The high energy data allow us to
detect the presence of a high energy cut-off and to study its evolution during
the outburst rise. This high energy feature is generally related to thermal
mechanisms in the framework of Comptonization models from which we can estimate
the plasma parameters. We found an electron temperature of about 30-40 keV and
an optical depth around 1.8-2.1. The high energy cut-off decreased along with
the radio flux, and disappeared as the jet turned off.Comment: 24 pages, 5 figures, accepted for publication in the Astrophsical
Journa
Studies of release properties of ISOLDE targets
Off-line release rates of Be, Mg, S, Mn and Kr from refractory materials were studied. Mn yields were determined from a ZrO2 target and Kr yields from a SrO and ZrO2 targets. A Monte Carlo code to optimize ISOLDE targets was introduced
State transition and flaring activity of IGR J17464-3213/H1743-322 with SPI/INTEGRAL telescope
IGR J17464-3213, already known as the HEAO-1 transient source H1743-322, has
been detected during a state transition by the SPI/INTEGRAL telescope. We
describe the spectral evolution and flaring activity of IGR
J17464-3213/H1743-322 from 2003 March 21 to 2003 April 22. During the first
part, the source followed a continuous spectral softening, with the peak of the
spectral energy distribution shifting from 100 keV down to a few keV. However
the thermal disk and the hard X-ray components had a similar intensity,
indicating that the source was in an intermediate state throughout our
observations and evolving toward the soft state. In the second part of our
observations, the ASM/RXTE and SPI/INTEGRAL light curve showed a strong flaring
activity. Two flare events lasting about 1 day each have been detected with SPI
and are probably due to instabilities in the accretion disk associated with the
state transition. During these flares, the low (1.5-12 keV) and high (20-200
keV) energy fluxes monitored with ASM/RXTE and SPI/INTEGRAL, are correlated and
the spectral shape (above 20 keV) remains unchanged while the luminosity
increases by a factor greater than 2.Comment: 26 pages, 7 figures, accepted for publication in Astrophysical
Journa
Monte Carlo simulations of global Compton cooling in inner regions of hot accretion flows
Hot accretion flows such as advection-dominated accretion flows are generally
optically thin in the radial direction. Thus photons generated at some radii
can cool or heat electrons at other radii via Compton scattering. Such global
Compton scattering has previously been shown to be important for the dynamics
of accretion flows. Here, we extend previous treatments of this problem by
using accurate global general relativistic Monte Carlo simulations. We focus on
an inner region of the accretion flow (R < 600R_g), for which we obtain a
global self-consistent solution. As compared to the initial, not
self-consistent solution, the final solution has both the cooling rate and the
electron temperature significantly reduced at radii >=10 gravitational radii.
On the other hand, the radiation spectrum of the self-consistent solution has
the shape similar to that of the initial iteration, except for the high-energy
cut-off being at an energy lower by a factor of ~2 and the bolometric
luminosity decreased by a factor of ~2. We also compare the global Compton
scattering model with local models in spherical and slab geometry. We find that
the slab model approximates the global model significantly better than the
spherical one. Still, neither local model gives a good approximation to the
radial profile of the cooling rate, and the differences can be up to two orders
of magnitude. The local slab model underestimates the cooling rate at outer
regions whereas it overestimates that rate at inner regions. We compare our
modelling results to observed hard-state spectra of black-hole binaries and
find an overall good agreement provided any disc outflow is weak. We find that
general-relativistic effects in flows which dynamics is modified by global
Comptonization is crucial in approaching this agreement.Comment: 9 pages, 4 figures. Accepted to MNRAS. Add a new section to discuss
on the impact of outflow and viscous electron heatin
Correlated optical, X-ray, and $-ray flaring activity seen with INTEGRAL during the 2015 outburst of V404 Cygni
Reproduced with permission from Astronomy & Astrophysics. © 2015 ESO.After 25 years of quiescence, the microquasar V404 Cyg entered a new period of activity in June 2015. This X-ray source is known to undergo extremely bright and variable outbursts seen at all wavelengths. It is therefore an object of prime interest to understand the accretion-ejection connections. These can, however, only be probed through simultaneous observations at several wavelengths. We made use of the INTEGRAL instruments to obtain long, almost uninterrupted observations from 2015 June 20th, 15:50 UTC to June 25th, 4:05 UTC, from the optical V-band, up to the soft γ-rays. V404 Cyg was extremely variable in all bands, with the detection of 18 flares with fluxes exceeding 6 Crab (20--40 keV) within 3 days. The flare recurrence can be as short as ∼ 20~min from peak to peak. A model-independent analysis shows that the >6 Crab flares have a hard spectrum. A simple 10--400 keV spectral analysis of the off-flare and flare periods shows that the variation in intensity is likely to be due to variations of a cut-off power law component only. The optical flares seem to be at least of two different types: one occurring in simultaneity with the X-ray flares, the other showing a delay greater than 10 min. The former could be associated with X-ray reprocessing by either an accretion disk or the companion star. We suggest that the latter are associated with plasma ejections that have also been seen in radio.Peer reviewe
The infrared/X-ray correlation of GX 339-4: Probing hard X-ray emission in accreting black holes
GX 339-4 has been one of the key sources for unravelling the accretion
ejection coupling in accreting stellar mass black holes. After a long period of
quiescence between 1999 and 2002, GX 339-4 underwent a series of 4 outbursts
that have been intensively observed by many ground based observatories [radio,
infrared(IR), optical] and satellites (X-rays). Here, we present results of
these broad-band observational campaigns, focusing on the optical-IR
(OIR)/X-ray flux correlations over the four outbursts. We found tight OIR/X-ray
correlations over four decades with the presence of a break in the IR/X-ray
correlation in the hard state. This correlation is the same for all four
outbursts. This can be interpreted in a consistent way by considering a
synchrotron self-Compton origin of the X-rays in which the break frequency
varies between the optically thick and thin regime of the jet spectrum. We also
highlight the similarities and differences between optical/X-ray and IR/X-ray
correlations which suggest a jet origin of the near-IR emission in the hard
state while the optical is more likely dominated by the blackbody emission of
the accretion disc in both hard and soft state. However we find a non
negligible contribution of 40 per cent of the jet emission in the V-band during
the hard state.
We finally concentrate on a soft-to-hard state transition during the decay of
the 2004 outburst by comparing the radio, IR, optical and hard X-rays light
curves. It appears that unusual delays between the peak of emission in the
different energy domains may provide some important constraints on jet
formation scenario.Comment: Accepted for publication in MNRAS, 12 pages, 8 figure
The INTEGRAL Galactic bulge monitoring program: the first 1.5 years
The Galactic bulge region is a rich host of variable high-energy point
sources. Since 2005, February 17 we are monitoring the source activity in this
region about every three days with INTEGRAL. Thanks to the large field of view,
the imaging capabilities and the sensitivity at hard X-rays, we are able to
present for the first time a detailed homogeneous (hard) X-ray view of a sample
of 76 sources in the Galactic bulge region. We describe the successful
monitoring program and show the first results for a period of about one and a
half year. We focus on the short (hour), medium (month) and long-term (year)
variability in the 20-60 keV and 60-150 keV bands. When available, we discuss
the simultaneous observations in the 3-10 keV and 10-25 keV bands. Per
visibility season we detect 32/33 sources in the 20-60 keV band and 8/9 sources
in the 60-150 keV band. On average, we find per visibility season one active
bright (>~100 mCrab, 20-60 keV) black-hole candidate X-ray transient and three
active weaker (<~25 mCrab, 20-60 keV) neutron star X-ray transients. Most of
the time a clear anti-correlation can be seen between the soft and hard X-ray
emission in some of the X-ray bursters. Hard X-ray flares or outbursts in X-ray
bursters, which have a duration of the order of weeks, are accompanied by soft
X-ray drops. On the other hand, hard X-ray drops can be accompanied by soft
X-ray flares/outbursts. We found a number of new sources, IGR J17354-3255, IGR
17453-2853, IGR J17454-2703, IGR J17456-2901b, IGR J17536-2339, and IGR
J17541-2252. We report here on some of the high-energy properties of these
sources. The high-energy light curves of all the sources in the field of view,
and the high-energy images of the region, are made available through the WWW at
http://isdc.unige.ch/Science/BULGE/.Comment: 27 pages, 42 figures, accepted for publication in A&A. Abstract
abridged. Tables 3,4,6,7 appear at the end. Images have been compressed and
are reduced in quality; original PostScript images can be retrieved from
http://isdc.unige.ch/~kuulkers/bulge
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