arXiv subjects

M. Revnivtsev

Publications and source records attributed to M. Revnivtsev.

At least 73 records · Page 4Linked to original sources

arXiv2004

INTEGRAL observations of five sources in the Galactic Center region

A number of new X-ray sources (IGR J17091-3624, IGR/XTE J17391-3021, IGR J17464-3213 (= XTE J17464-3213 = H 1743-322), IGR J17597-2201, SAX/IGR J18027-2017) have been observed with the INTEGRAL observatory during ultra deep exposure of the Galactic Center region in August-September 2003. Most of them were permanently visible by the INTEGRAL at energies higher than $\sim 20$ keV, but IGR/XTE J17391-3021 was observed only during its flaring activity with a flux maximum of $\sim120$ mCrab. IGR J17091-3624, IGR J17464-3213 and IGR J17597-2201 were detected up to $\sim 100$-150 keV. In this paper we present the analysis of INTEGRAL observations of these sources to determine the nature of these objects. We conclude that all of them have a galactic origin. Two sources are black hole candidates (IGR J17091-3624 and IGR J17464-3213), one is an LMXB neutron star binary (presumably an X-ray burster) and two other sources (IGR J17597-2201 and SAX/IGR J18027-2017) are neutron stars in high mass binaries; one of them (SAX/IGR J18027-2017) is an accreting X-ray pulsar.

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arXiv2004

INTEGRAL detection of a long powerful burst from SLX1735-269

We present results of analysis of a bursting behavior of a low mass X-ray binary system SLX 1735-269 during INTEGRAL observations of the Galactic Center region in 2003. There were detected 6 type I X-ray bursts in total, with one being much longer and more powerful then others. A strong dependence of the bursts recurrence time on the mass accretion rate is observed, that is likely caused by the change in the burning regime. The long burst demonstrated a photospheric radius expansion. We discuss possible scenarios of this long burst and show that it is unlikely a carbon burning flash and rather a burst of large pile of hydrogen and helium accelerated by electron capture processes in a dense accumulated layer.

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arXiv2004

Variability of X-ray pulsars in a hard energy band observed with INTEGRAL

We present the first results of the observations of the X-ray pulsars LMC X-4, 4U0352+309 and EXO1722-363 performed with the INTEGRAL observatory. The LMC X-4 was investigated during the whole superorbital cycle ($\sim$30 days) and it was found that its period was not stable at this time scale. We detected a variable X-ray flux (18-60 keV) from the pulsar EXO1722-363, which could be connected with the orbital motion in the binary system. A more accurate position and the estimate of the orbital period for this source are reported. We also investigated a hard X-ray spectrum of 4U0352+309 (X Persei) measured with INTEGRAL and report the detection of the cyclotron absorption line at about 29 keV.

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arXiv2004

Broadband X-ray spectrum of GRS 1734-292, a luminous Seyfert 1 galaxy behind the Galactic Center

Based on a deep survey of the Galactic Center region performed with the INTEGRAL observatory, we measured for the first time the hard X-ray (20-200 keV) spectrum of the Seyfert 1 galaxy GRS 1734-292 located in the direction of the Galactic Center. We extended the spectrum to lower energies using archival GRANAT and ASCA observations. The broadband X-ray spectrum is similar to those of other nearby luminous AGNs, having a power law shape without cutoff up to at least 100 keV.

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arXiv2004

First simultanous X-ray and optical observations of rapid variability of supercritical accretor SS433

We present results of first simultaneous optical and X-ray observations of peculiar binary system SS433. For the first time, chaotic variability of SS433 in the optical spectral band (R band) on time scales as small as tens of seconds was detected. We find that the X-ray flux of SS433 is delayed with respect to the optical emission by approximately 80 sec. Such a delay can be interpreted as the travel time of mass accretion rate perturbations from the jet base to the observed X-ray emitting region. In this model, the length of the supercritical accretion disk funnel in SS433 is ~1e12 cm.

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arXiv2004

RXTE broadband X-ray spectra of intermediate polars and white dwarf mass estimates

We present results of an analysis of broadband spectra of 14 intermediate polars obtained with the RXTE observatory (PCA and HEXTE spectrometers, 3-100 keV). By means of our calculations of the structure and the emergent spectrum of the post-shock region of intermediate polars we fitted the observed spectra and obtained estimates of the white dwarf masses. The estimated masses are compared with masses obtained by other authors.

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arXiv2004

Broadband X-ray spectrum of intermediate polar V1223 Sgr

We present the broadband phase averaged spectrum of one of the brightest intermediate polars V1223 Sgr, obtained with INTEGRAL and RXTE observatories (3-100 keV). Good statistical quality of the spectrum in a hard X-ray energy band (INTEGRAL/IBIS and RXTE/HEXTE) allowed us to disentangle contributions of a direct optically thin plasma emission and a reflected component to the spectrum of V1223 Sgr. The obtained measurement of the post-shock temperature of the accreting matter give us the information about the mass of the white dwarf and the inclination of the system.

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arXiv2004

RXTE all-sky slew survey. Catalog of X-ray sources at |b|>10deg

We report results of a serendipitous hard X-ray (3--20 keV), nearly all-sky (|b|>10deg) survey based on RXTE/PCA observations performed during satellite reorientations in 1996--2002. The survey is 80% (90%) complete to a 4$σ$ limiting flux of ~1.8 (2.5) e-11 erg/s/cm2 in the 3--20 keV band. The achieved sensitivity in the 3--8 keV and 8--20 keV subbands is similar to and an order of magnitude higher than that of the previously record HEAO-1 A1 and HEAO-1 A4 all-sky surveys, respectively. A combined 7000 sq. deg area of the sky is sampled to flux levels below 1e-11 erg/s/cm2 (3--20 keV). In total 294 sources are detected and localized to better than 1 deg. 236 (80%) of these can be confidently associated with a known astrophysical object; another 22 likely result from the superposition of 2 or 3 closely located known sources. 35 detected sources remain unidentified, although for 12 of these we report a likely soft X-ray counterpart from the ROSAT all-sky survey bright source catalog. Of the reliably identified sources, 63 have local origin (Milky Way, LMC or SMC), 64 are clusters of galaxies and 100 are active galactic nuclei (AGN). The fact that the unidentified X-ray sources have hard spectra suggests that the majority of them are AGN, including highly obscured ones (nH>1e23 cm^{-2}). For the first time we present a logN-logS diagram for extragalactic sources above 4e-12 erg/s/cm2 at 8-20 keV.

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arXiv2004

A Hard X-ray survey of the Galactic Center with INTEGRAL/IBIS. Catalog of sources

During the period Aug.23-Sept.24 2003, the INTEGRAL observatory performed an ultra deep survey of the Galactic Center region with a record sensitivity at energies higher than 20 keV. We have analized images of the Galactic Center region obtained with the ISGRI detector of the IBIS telescope (15-200 keV) and present here a catalog of detected sources. In total, 60 sources with a flux higher than 1.5 mCrab have been detected. 44 of them were earlier identified as Galactic binary systems, 3 are extragalactic objects. 2 new sources are discovered.

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arXiv2003

Doppler broadening of the iron line and R-Gamma correlation in black hole binaries

RXTE/PCA observations of several black hole X-ray binaries in the low spectral state revealed a tight correlation between spectral parameters and characteristic frequencies of variability of X-ray flux. In particular, the amplitude of reflection increases and the slope of Comptonized radiation steepens as the noise frequencies increase. The data also suggest that there is a correlated increase of the width of the Fe fluorescent line, probably related to the Doppler broadening of the reflection features. Moreover, the width of the line seems to follow DeltaE/E ~ nu_qpo^{1/3} law. If confirmed with higher energy resolution observations, this result will have significant impact on the models of the accretion flow and on our understanding of the nature of characteristic frequencies of variability in X-ray binaries. In particular, it will lend support to the truncated disk picture, confirming that the spectral variations are indeed related to changes of the position of the inner disk boundary and that characteristic variability frequencies are proportional to the Keplerian frequency at the inner boundary of the accretion disk.

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arXiv2003

The spectrum of the cosmic X-ray background observed by RTXE/PCA

We have analyzed a large set of RXTE/PCA scanning and slewing observations performed between April 1996 and March 1999. We obtained the 3-20 keV spectrum of the cosmic X-ray background (CXB) by subtracting Earth-occulted observations from observations of the X-ray sky at high galactic latitude and far away from sources. The sky coverage is approximately ~22600 sq.deg. The PCA spectrum of CXB in 3-20 keV energy band is adequately approximated by a single power law with photon index Gamma~1.4 and normalization at 1 keV ~9.5 phot/s/cm2/keV/sr. Instrumental background uncertainty precludes accurate RXTE/PCA measurements of the spectrum of cosmic X-ray background at energies above 15 keV and therefore we can not detect the high energy cutoff observed by HEAO-1 A2 experiment. Deep observations of the 6 high latitude points used to model the PCA background provide a coarse measure of the spatial variation of the CXB. The CXB variations are consistent with a fixed spectral shape and variable normalization characterized by a fractional rms amplitude of ~7% on angular scales of ~1 square deg.

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arXiv2003

Distribution of the Galactic Bulge emission at |b|>2deg according to the RXTE Galactic Center scans

We present an analysis of the Galactic bulge emission observed by the RXTE/PCA during a set of scans over the Galactic Center field, performed in 1999-2001. The total exposure time of these observations is close to 700 ksec. We construct the distribution of Galactic ridge emission intensity and spectral parameters up to Galactic latitudes b=-10deg;+9deg. We show that the intensity distribution of the ridge emission at |b|>2deg could be well described by an exponential model with e-folding width b_0~ 3.3deg. Best-fit spectral parameters do not show statistically significant changes over Galactic latitude

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arXiv2003

Boundary layer, accretion disk and X-ray variability in luminous LMXBs

Using Fourier frequency resolved X-ray spectroscopy we study short term spectral variability in luminous LMXBs. With RXTE/PCA observations of 4U1608--52 and GX340+0 on the horizontal/normal branch of the color-intensity diagram we show that aperiodic and quasiperiodic variability on ~ sec-msec time scales is caused primarily by variations of the luminosity of the boundary layer. The emission of the accretion disk is less variable on these time scales and its power density spectrum follows Pdisk(f) ~ 1/f law, contributing to observed flux variation at low frequencies and low energies only. The kHz QPOs have the same origin as variability at lower frequencies, i.e. independent of the nature of the "clock", the actual luminosity modulation takes place on the neutron star surface, The boundary layer spectrum remains nearly constant in the course of the luminosity variations and is represented to certain accuracy by the Fourier frequency resolved spectrum. In the considered range Mdot ~ (0.1-1)Mdot_Edd it depends weakly on the global mass accretion rate and in the limit Mdot ~ Mdot_Edd is close to Wien spectrum with kT ~ 2.4 keV (in the distant observer's frame). The spectrum of the accretion disk emission is significantly softer and in the 3--20 keV range is reasonably well described by a relativistic disk model with a mass accretion rate consistent with the value inferred from the observed X-ray flux.

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arXiv2003

First results of observations of transient pulsar SAXJ2103.5+4545 with the INTEGRAL observatory

We present preliminary results of observations of X-ray pulsar SAX J2103.5+4545 with INTEGRAL observatory in Dec 2002. Maps of this sky region in energy bands 3-10, 15-40, 40-100 and 100-200 keV are presented. The source is significantly detected up to energies of $\sim100$ keV. The hard X-ray flux in the 15-100 energy band is variable, that could be connected with the orbital phase of the binary system. We roughly reconstructed the source spectrum using its comparison to that of Crab nebula. It is shown that the parameters of the source spectrum in 18-150 keV energy range are compatible with that obtained earlier by RXTE observatory

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arXiv2003

RXTE observations of strongly absorbed sources IGR J16318-4848 and IGR J16358-4726

Results of analysis of RXTE observations of strongly absorbed X-ray sources IGR J16318-4848 and IGR J16358-4726 are presented. Careful subtraction of Galactic ridge emission contribution to the observed spectra of RXTE/PCA allowed us to obtain the spectra of the sources in 3-25 keV energy band. Spectra of the sources cold be well described by a power law with photoabsorption. It is shown that the value of absorption column in the case of RXTE observation of IGR J16318-4848 performed on March 14.1, 2003 is somewhat higher that that obtained by XMM observatory on Feb 10.7 2003. This could imply that the source has variable absorption, presumably connected with an orbital phase of the binary system. It is noted, that all three X-ray sources, discovered by INTEGRAL observatory in the sky region of (l,b)~(336,0) (IGR J16318-4848, IGR J16320-4751 and IGR J16358-4726) have large intrinsic photoabsorption and could be high mass X-ray binaries. This hypothesis has indirect support from the fact that their are located close to the Norma spiral arm tangent, i.e. in the region of enhanced concentrations of young massive stars. If they are reside within this spiral arm some rough estimation of the sources distance could be made -- D~6-8 kpc.

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arXiv2003

IGR J16318-4848: an X-ray source in a dense envelope?

The hard X-ray source IGR J16318-4848 was recently discovered by the INTEGRAL observatory (Courvoisier et al.) and subsequently uncovered in archival data of ASCA observations in 1994 (Murakami et al.). We present results of a detailed analysis of the ASCA data. The spectrum of the source in the 0.5--10 keV band is extraordinarily hard and is virtually unobservable below 4 keV because of strong photoabsorption NHL L>4e23 cm^-2. The 4--10 keV emission is dominated by a Kalpha line of neutral or weakly ionized iron with an equivalent width of \~2.5 keV. There is also an indication for a second line at ~7 keV. Our analysis of archival observations of the IGR J16318-4848 infrared counterpart, discovered by Foschini et al., shows that the point source is detected at different wavelengths in the 1--15 micron range. The available data suggest that IGR J16318-4848 is an X-ray binary system enshrouded by a dense envelope. It is possible that the source is a wind-fed high-mass X-ray binary similar to GX 301-2. We argue that IGR J16318-4848 might be the first representative of a previously unknown population of highly absorbed galactic X-ray sources, which remained undetected with X-ray missions before INTEGRAL.

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arXiv2002

Super-Eddington outburst of V4641 Sgr

X-ray transients provide unique opportunity to probe accretion regimes of at a vastly different accretion rates. We analyze a collection of the RXTE observations (Galactic Center scans, ASM monitoring and a pointed observation) of enigmatic transient source high mass X-ray binary V4641 Sgr and argue that they broadly support the hypothesis that giant September 1999 outburst was associated with an episode of super-Eddington accretion onto the black hole. During the outburst an extended optically thick envelope/outflow has been formed around the source making the observational appearance of V4641 Sgr in many aspects very similar to that of SS433. These results suggest that objects like V4641 Sgr and SS433 indeed represent the class of objects accreting matter at a rate comparable or above Eddington value and the formation of an envelope/outflow is a generic characteristic of supercritical accretion. When the accretion rate decreased the envelope vanished and the source short term variability and spectral properties started to resemble those of other galactic black hole candidates accreting at a rate well below the Eddington value. Interestingly that during this phase the source spectrum was very similar to the Cygnus X-1 spectrum in the low state inspite of more than order of magnitude larger X-ray luminosity.

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arXiv2001

Reflection and noise in the low spectral state of GX339-4

We analyze RXTE/PCA observations of GX339-4 in the low spectral state from 1996--1997 and show that the pattern of its spectral and temporal variability is nearly identical to that of Cyg X-1. In particular, a tight correlation exists between the QPO centroid frequency and the spectral parameters. An increase of the QPO centroid frequency is accompanied with an increase of the amplitude of the reflected component and a steepening the slope of the underlying power law. Fourier frequency resolved spectral analysis showed, that the variability of the reflected component at frequencies higher than ~1-10 Hz is suppressed in comparison with that of the primary emission.

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