arXiv subjects

S. S. Tsygankov

Publications and source records attributed to S. S. Tsygankov.

52 records · Page 3Linked to original sources

arXiv2013

Identification of Four X-ray Sources from the INTEGRAL and Swift Catalogs

Four hard X-ray sources from the INTEGRAL and Swift catalogs have been identified. X-ray and optical spectra have been obtained for each of the objects being studied by using data from the INTEGRAL, Swift, ROSAT, and Chandra X-ray observatories as well as observations with the RTT-150 and AZT-33IK optical telescopes. Two sources (SWIFT J1553.6+2606 and SWIFT J1852.2+8424) are shown to be extragalactic in nature: the first is a quasar, while the registered X-ray flux from the second is the total emission from two Seyfert 1 galaxies at redshifts 0.1828 and 0.2249. The source IGR J22534+6243 resides in our Galaxy and is an X-ray pulsar with a period of ~46.674 s that is a member of a high-mass X-ray binary, probably with a Be star. The nature of yet another Galactic source, SWIFT J1852.8+3002, is not completely clear and infrared spectroscopy is needed to establish it.

astro-ph.HE↗

arXiv2013

On Timing and Spectral Characteristics of the X-ray Pulsar 4U 0115+63: Evolution of the Pulsation Period and the Cyclotron Line Energy

An overview of the results of observations for the transient X-ray pulsar 4U 0115+63, a member of a binary system with a Be star, since its discovery to the present day (~40 years) based on data from more than dozen observatories and instruments is presented. A overall light curve and the history of change in the spin frequency of the neutron star over the entire history of its observations, which also includes the results of recent measurements made by the INTEGRAL observatory during the 2004, 2008, and 2011 outbursts, are provided. The source's energy spectra have also been constructed from the INTEGRAL data obtained during the 2011 outburst for a dynamic range of its luminosities (~10^{37} - 7 x 10^{37} erg/s). We show that apart from the fundamental harmonic of the cyclotron absorption line at energy ~11 keV, its four higher harmonics at energies ~24, 35.6, 48.8, and 60.7 keV are detected in the spectrum. We have performed a detailed analysis of the source's spectra in the 4-28 keV energy band based on all of the available RXTE archival data obtained during bright outbursts in 1995-2011. We have confirmed that modifying the source's continuum model can lead to the disappearance of the observed anticorrelation between the energy of the fundamental harmonic of the cyclotron absorption line and the source's luminosity. Thus, the question about the evolution of the cyclotron absorption line energy with the luminosity of the X-ray pulsar 4U 0115+63 remains open and a physically justified radiation model for X-ray pulsars is needed to answer it.

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arXiv2013

Population of persistent high mass X-ray binaries in the Milky Way

We present results of the study of persistent high mass X-ray binaries (HMXBs) in the Milky Way, obtained from the deep INTEGRAL Galactic plane survey. This survey provides us a new insight into the population of high mass X-ray binaries because almost half of the whole sample consists of sources discovered with INTEGRAL. It is demonstrated for the first time that the majority of persistent HMXBs have supergiant companions and their luminosity function steepens somewhere around ~2x10^{36} erg/s. We show that the spatial density distribution of HMXBs correlates well with the star formation rate distribution in the Galaxy. The vertical distribution of HMXBs has a scale-height h~85 pc, that is somewhat larger than the distribution of young stars in the Galaxy. We propose a simple toy model, which adequately describes general properties of HMXBs in which neutron stars accrete a matter from the wind of the its companion (wind-fed NS-HMXBs population). Using the elaborated model we argue that a flaring activity of so-called supergiant fast X-ray transients, the recently recognized sub-sample of HMXBs, is likely related with the magnetic arrest of their accretion.

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arXiv2012

Hard X-ray emission lines from the decay of Ti-44 in the remnant of supernova 1987A

It is assumed that the radioactive decay of Ti-44 powers the infrared, optical and UV emission of supernova remnants after the complete decay of Co-56 and Co-57 (the isotopes that dominated the energy balance during the first three to four years after the explosion) until the beginning of active interaction of the ejecta with the surrounding matter. Simulations show that the initial mass of Ti-44 synthesized in core-collapse supernovae is (0.02-2.5) x 10^{-4} solar masses (M_sun). Hard X-rays and gamma-rays from the decay of this Ti-44 have been unambiguously observed from Cassiopeia A only, leading to the suggestion that the values of the initial mass of Ti-44 near the upper bound of the predictions occur only in exceptional cases. For the remnant of supernova 1987A, an upper limit to the initial mass of Ti-44 of < 10^{-3} M_sun has been obtained from direct X-ray observations, and an estimate of (1-2) x 10^{-4} M_sun has been made from infrared light curves and ultraviolet spectra by complex model-dependent computations. Here we report observations of hard X-rays from the remnant of supernova 1987A in the narrow band containing two direct-escape lines of Ti-44 at 67.9 and 78.4 keV. The measured line fluxes imply that this decay provided sufficient energy to power the remnant at late times. We estimate that the initial mass of Ti-44 was (3.1+/-0.8) x 10^{-4} M_sun, which is near the upper bound of theoretical predictions.

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arXiv2012

Deep Hard X-ray Survey of the Large Magellanic Cloud

Results of the deep survey of the Large Magellanic Cloud (LMC), performed with the INTEGRAL observatory, are presented. The long exposure (~7 Ms) allowed us to detect twenty one sources in this sky region: ten belonging to the LMC itself (7 HMXBs, 2 PSRs, 1 LMXB), six of extragalactic origin and three belonging to other galaxies from the Local Group - the Milky Way (2 sources) and Small Magellanic Cloud (1 source). Four new hard X-ray sources of these 21 ones were discovered during the survey in addition to IGR J05414-6858 reported earlier; two of them were identified with extragalactic objects. We report also for the first time the detection of a hard X-ray emission from the Crab-like pulsar PSR J0537-6910 and identification of the hard X-ray source IGR J05305-6559 with the high-mass X-ray binary EXO 053109-6609.

astro-ph.HE↗

arXiv2012

Luminosity Function of High-Mass X-ray Binaries and Anisotropy in the Distribution of Active Galactic Nuclei toward the Large Magellanic Cloud

In 2003-2012, the INTEGRAL observatory has performed long-term observations of the Large Magellanic Cloud (LMC). At present, this is one of the deepest hard X-ray (20-60 keV) surveys of extragalactic fields in which more than 20 sources of different natures have been detected. We present the results of a statistical analysis of the population of high-mass X-ray binaries in the LMC and active galactic nuclei (AGNs) observed in its direction. The hard X-ray luminosity function of high-mass X-ray binaries is shown to be described by a power law with a slope alpha~1.8, that in agreement with the luminosity function measurements both in the LMC itself, but made in the soft X-ray energy band, and in other galaxies. At the same time, the number of detected AGNs toward the LMC turns out to be considerably smaller than the number of AGNs registered in other directions, in particular, toward the source 3C 273. The latter confirms the previously made assumption that the distribution of matter in the local Universe is nonuniform.

astro-ph.HE↗

arXiv2009

Timing Characteristics of the Hard X-ray Emission from Bright X-ray Pulsars Based on INTEGRAL Data

We review the results of a timing analysis of the observations for ten bright X-ray pulsars (with fluxes >100 mCrab in the 20-100 keV energy band) that fell within the INTEGRAL field of view from 2003 to 2007. The dependence of the pulse profile on the energy and intrinsic source luminosity has been investigated; particular attention has been paid to searching for changes in the pulse profile near the cyclotron frequency. The dependence of the pulsed fraction for X-ray pulsars on their luminosity and energy band has been studied in detail for the first time.

astro-ph.HE↗

arXiv2008

Discovery of X-ray Pulsations from the HMXB Source AXJ1749.1-2733

We are reporting a discovery of X-ray pulsations from the source AX J1749.1-2733 with the period of ~132 s based on the XMM-Newton data obtained in March 2007. The observed pulse profile has a double-peaked structure with the pulse fraction of about 25-30 % in the 3-10 keV energy band. We have also found that a periodicity with practically the same period has been detected from the source by the IBIS telescope onboard the INTEGRAL observatory during an outburst on Sept. 9, 2003 in the 20-50 keV energy band. Due to the double-peaked pulse profile, there is an additional peak on both periodograms of nearly ~66 s, therefore we have also investigated the possibility that the last value is the true pulse period. The source spectrum obtained by the XMM-Newton observatory in the soft energy band is being heavily absorbed ($N_H\simeq2\times10^{23}$ cm$^{-2}$) due to a strong intrinsic absorption in the binary system that leads to the conclusion that AX J1749.1-2733 is a new transient X-ray pulsar in the high mass X-ray binary system.

astro-ph↗

arXiv2007

4U 0115+63 from RXTE and INTEGRAL Data: Pulse Profile and Cyclotron Line Energy

We analyze the observations of the transient X-ray pulsar 4U 0115+63 with the RXTE and INTEGRAL observatories in a wide X-ray (3-100 keV) energy band during its intense outbursts in 1999 and 2004. The energy of the fundamental harmonic of the cyclotron resonance absorption line near the maximum of the X-ray flux from the source (luminosity range 5x10^{37} - 2x10^{38} erg/s) is ~11 keV. When the pulsar luminosity falls below ~5x10^{37} erg/s, the energy of the fundamental harmonic is displaced sharply toward the high energies, up to ~16 keV. Under the assumption of a dipole magnetic field configuration, this change in cyclotron harmonic energy corresponds to a decrease in the height of the emitting region by ~2 km, while other spectral parameters, in particular, the cutoff energy, remain essentially constant. At a luminosity ~7x10^{37} erg/s, four almost equidistant cyclotron line harmonics are clearly seen in the spectrum. This suggests that either the region where the emission originates is compact or the emergent spectrum from different (in height) segments of the accretion column is uniform. We have found significant pulse profile variations with energy, luminosity, and time. In particular, we show that the profile variations from pulse to pulse are not reduced to a simple modulation of the accretion rate specified by external conditions.

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arXiv2006

Spectral analysis of X-ray pulsars with the INTEGRAL observatory

We studied spectra for 34 accretion-powered X-ray and one millisecond pulsars that were within the field of view of the INTEGRAL observatory over two years (December 2002 - January 2005) of its in-orbit operation and that were detected by its instruments at a statistically significant level (>8 sigma in the energy range 18-60 keV). There are seven recently discovered objects of this class among the pulsars studied: 2RXP J130159.6-635806, IGR/AX J16320-4751, IGR J16358-4726, AX J163904-4642, IGR J16465-4507, SAX/IGR J18027-2017 and AX J1841.0-0535. We analyze the evolution of spectral parameters as a function of the intensity of the sources and compare these with the results of previous studies.

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arXiv2006

V0332+53 in the outburst of 2004--2005: luminosity dependence of the cyclotron line and pulse profile

We present results of observations of the transient X-ray pulsar V0332+53 performed during a very powerful outburst in Dec, 2004 -- Feb, 2005 with the INTEGRAL and RXTE observatories in a wide (3-100 keV) energy band. A cyclotron resonance scattering line at an energy of ~26 keV has been detected in the source spectrum together with its two higher harmonics at ~50 and ~73 keV, respectively. We show that the energy of the line is not constant but linearly changes with the source luminosity. Strong pulse profile variations, especially near the cyclotron line, are revealed for different levels of the source intensity. We discuss the obtained results in terms of the theoretical models of X-ray pulsars.

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arXiv2005

Hard Spectra of X-Ray Pulsars from INTEGRAL Data

We present spectra for 34 accretion-powered X-ray and one millisecond pulsars that were within the field of view of the INTEGRAL observatory over two years (December 2002 - January 2005) of its in-orbit operation and that were detected by its instruments at a statistically significant level (> 8 sigma in the energy range 18--60 keV). There are seven recently discovered objects of this class among the pulsars studied: 2RXP J130159.6-635806, IGR/AX J16320-4751, IGR J16358-4726, AX J163904-4642, IGR J16465-4507, SAX/IGR J18027-2017 and AX J1841.0-0535. We have also obtained hard X-ray (> 20 keV) spectra for the accretion-powered pulsars A 0114+650, RX J0146.9+6121, AX J1820.5-1434, AX J1841.0-0535 and the millisecond pulsar XTE J1807-294 for the first time. We analyze the evolution of spectral parameters as a function of the intensity of the sources and compare these with the results of previous studies.

astro-ph↗

arXiv2005

Long-Term INTEGRAL and RXTE Observations of the X-Ray Pulsar LMC X-4

We analyze the observations of the X-ray pulsar LMC X-4 performed by the INTEGRAL observatory and the All-Sky Monitor (ASM) of the RXTE observatory over a wide energy range. The observed hard X-ray flux from the source is shown to change by more than a factor of 50 (from ~70 mCrab in the high state to ~1.3 mCrab in the low state) on the time scale of the accretion-disk precession period, whose mean value for 1996-2004 was determined with a high accuracy, Pprec=30.275+/-0.004 days. In the low state, a flare about 10 h in duration was detected from the source; the flux from the source increased by more than a factor of 4 during this flare. The shape of the pulsar's broadband spectrum is essentially invariable with its intensity; no statistically significant features associated with the possible resonance cyclotron absorption line were found in the spectrum of the source.

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arXiv2005

Observations of the Transient X-ray Pulsar KS 1947+300 by the INTEGRAL and RXTE Observatories

We analyze the observations of the X-ray pulsar KS 1947+300 performed by the INTEGRAL and RXTE observatories over a wide (3-100 keV) X-ray energy range. The shape of the pulse profile was found to depend on the luminosity of the source. Based on the model of a magnetized neutron star, we study the characteristics of the pulsar using the change in its spin-up rate. We estimated the magnetic field strength of the pulsar and the distance to the binary.

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arXiv2004

Observations of the X-ray Pulsar GX 301-2 with the ART-P Telescope of the Granat Observatory

The variability of the X-ray flux from the pulsar GX 301-2 is analyzed by using data from the ART-P telescope of the Granat Observatory. The intensity variations with time scales of several thousand seconds are studied at various orbital phases. The high-state flux from the source exceeds its low-state flux by as much as a factor of 10. The hardness and spectrum of the source are shown to change greatly with its intensity. These intensity variations are most likely caused by substantial inhomogeneities in the stellar wind from the companion star.

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arXiv2004

Two Years of Observations of the X-ray Pulsar SMC X-1 with the ART-P Telescope onboard the Granat Observatory

We present the observations of the pulsar SMC X-1 with the ART-P telescope onboard the Granat observatory. We investigate the variability of the flux from the source on time scales of several tens of days. The intensity variation of the pulsar are shown to be consistent with the presence of a periodicity in the system with a characteristic time scale of $\sim61$ days. The precession of an inclined accretion disk, as indirectly confirmed by the absence of low-state pulsations, may be responsible for the observed variability. The spectrum of the source is well described by a power-law energy dependence of the photon flux density with a slope of $\sim1.5$ and an exponential cutoff at energies above $\sim14-18$ keV. We estimated the inclinations between the planes of the orbit and the accretion disk and the magnetic field of the neutron star.

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