arXiv subjects

S. Yu. Sazonov

Publications and source records attributed to S. Yu. Sazonov.

35 records · Page 2Linked to original sources

arXiv2017

Optical Spectroscopy of Candidates for Quasars at 3<z<5.5 from the XMM-Newton X-ray survey. A distant X-ray Quasar at z=5.08

We present the results of optical spectroscopy for 19 quasar candidates at photometric redshifts $\zphot \gtrsim 3$, \Nobs \ of which enter into the Khorunzhev et al.~(2016) catalog (K16). This is a catalog of quasar candidates and known type 1 quasars selected among the X-ray sources of the \textit{3XMM-DR4}catalog of the XMM-Newton serendipitous survey. We have performed spectroscopy for a quasi-random sample of new candidates at the 1.6-m \Azt \ telescope of the Sayan Solar Observatory and the 6-m BTA telescope of the Special Astrophysical Observatory. The spectra at \Azt \ were taken with the new low- and medium-resolution ADAM spectrograph that was produced and installed on the telescope in 2015. Fourteen of the \Nobs \ candidates actually have turned out to be quasars; 10 of them are at spectroscopic redshifts z > 3. The high purity of the sample of new candidates suggests that the purity of the entire K16 catalog of quasars is probably 70--80\%. One of the most distant ($\zspec=5.08$) optically bright ($i^\prime\lesssim 21$) quasars ever detected in X-ray surveys has been discovered.

astro-ph.GA↗

arXiv2012

Masses and Accretion Rates of Supermassive Black Holes in Active Galactic Nuclei from the INTEGRAL Survey

The masses of 68 supermassive black holes (SMBHs) in nearby (z<0.15) active galactic nuclei (AGNs) detected by the INTEGRAL observatory in the hard X-ray energy band (17-60 keV) outside the Galactic plane (|b| > 5 degrees) have been estimated. Well-known relations between the SMBH mass and (1) the infrared luminosity of the stellar bulge (from 2MASS data) and (2) the characteristics of broad emission lines (from RTT-150 data) have been used. A comparison with the more accurate SMBH mass estimates obtained by the reverberation-mapping technique and from direct dynamical measurements is also made for several objects. The SMBH masses derived from the correlation with the bulge luminosity turn out to be systematically higher than the estimates made by other methods. The ratio of the bolometric luminosity to the critical Eddington luminosity has been found for all AGNs. It ranges from 1 to 100% for the overwhelming majority of objects.

astro-ph.CO↗

arXiv2012

SRG/eROSITA prospects for detection of GRB afterglows

We discuss the potential of the eROSITA telescope on board the \emph{Spectrum-X-Gamma} observatory to detect gamma-ray burst (GRB) X-ray afterglows during its 4-year all-sky survey. The expected rate of afterglows associated with long-duration GRBs without any information on the bursts proper that can be identified by a characteristic power-law light curve in the eROSITA data is 4--8 events per year. An additional small number, $\lesssim 2$ per year, of afterglows may be associated with short GRBs, ultra hard (GeV) GRBs and X-ray flashes. eROSITA can thus provide the first unbiased (unaffected by GRB triggering) sample of $\lesssim 40$ X-ray afterglows, which can be used for statistical studies of GRB afterglows and for constraining the shape of the GRB $\log N$--$\log S$ distribution at its low-fluence end. The total number of afterglows detected by eROSITA may be yet higher due to orphan afterglows and failed GRBs. The actual detection rate could thus provide interesting constraints on the properties of relativistic jets associated with collapse of massive stars. Finally, eROSITA can provide accurate ($\lesssim 30"$) coordinates of newly discovered afterglows within a day after the event, early enough for scheduling further follow-up observations.

astro-ph.HE↗

arXiv2012

X-ray line formation in the spectrum of SS 433

The mechanisms for the formation of X-ray lines in the spectrum of SS 433 are investigated by taking into account the radiative transfer inside the jets. The results of Monte Carlo numerical simulations are presented. The effect of a decrease in line intensity due to scattering inside the jet turns out to be pronounced, but it does not exceed 60% in magnitude on the entire grid of parameters. The line broadening due to scattering, nutational motion, and the contribution of satellites can lead to overestimates of the jet opening angle $Θ$ from the line widths in Chandra X-ray observations. The fine structure of the lines turns out to be very sensitive to the scattering effects. This makes its investigation by planned X-ray observatories equipped with high-resolution spectrometers (primarily Astro-H) a powerful tool for diagnosing the parameters of the jets in SS 433.

astro-ph.HE↗

arXiv2010

Polarization of X-ray lines from galaxy clusters and elliptical galaxies - a way to measure tangential component of gas velocity

We study the impact of gas motions on the polarization of bright X-ray emission lines from the hot intercluster medium (ICM). The polarization naturally arises from resonant scattering of emission lines owing to a quadrupole component in the radiation field produced by a centrally peaked gas density distribution. If differential gas motions are present then a photon emitted in one region of the cluster will be scattered in another region only if their relative velocities are small enough and the Doppler shift of the photon energy does not exceed the line width. This affects both the degree and the direction of polarization. The changes in the polarization signal are in particular sensitive to the gas motions perpendicular to the line of sight. We calculate the expected degree of polarization for several patterns of gas motions, including a slow inflow expected in a simple cooling flow model and a fast outflow in an expanding spherical shock wave. In both cases, the effect of non-zero gas velocities is found to be minor. We also calculate the polarization signal for a set of clusters, taken from large-scale structure simulations and evaluate the impact of the gas bulk motions on the polarization signal. We argue that the expected degree of polarization is within reach of the next generation of space X-ray polarimeters.

astro-ph.HE↗

arXiv2008

Optical identification of hard X-ray source IGRJ18257-0707

We present the results of the optical identification of hard X-ray source IGRJ18257-0707 trough the spectroscopic observations of its optical counterpart with RTT150 telescope. Accurate position of the X-ray source, determined using Chandra observations, allowed us to associate this source with the faint optical object (m_R=~20.4), which shows broad H_αemission line in its optical spectrum. Therefore we conclude that the source IGRJ18257-0707 is a type 1 Seyfert galaxy at redshift z=0.037.

astro-ph↗

arXiv2008

Optical Identifications of Five INTEGRAL Hard X-ray Sources in the Galactic Plane Region

The results of optical identifications of five hard X-ray sources in the Galactic plane region from the INTEGRAL all-sky survey are presented. The X-ray data on one source (IGRJ20216+4359) are published for the first time. The optical observations were performed with 1.5-m RTT-150 telescope (TUBITAK National Observatory, Antalya, Turkey) and 6-m BTA telescope (Special Astrophysical Observatory, Nizhny Arkhyz, Russia). A blazar, three Seyfert galaxies, and a high-mass X-ray binary are among the identified sources.

astro-ph↗

arXiv2008

Several New Active Galactic Nuclei Among X-ray Sources Detected by INTEGRAL and SWIFT Observatories

We present the results of the optical identifications of a set of X-ray sources from the all-sky surveys of INTEGRAL and SWIFT observatories. Optical data were obtained with Russian-Turkish 1.5-m Telescope (RTT150). Nine X-ray sources were identified as active galactic nuclei (AGNs). Two of them are hosted by nearby, nearly exactly edge-on, spiral galaxies MCG -01-05-047 and NGC 973. One source, IGR J16562-3301, is most probably BL Lac object (blazar). Other AGNs are observed as stellar-like nuclei of spiral galaxies, with broad emission lines in their spectra. For the majority of our hard X-ray selected AGNs, their hard X-ray luminosities are well-correlated with the luminosities in [OIII],5007 optical emission line. However, the luminosities of some AGNs deviate from this correlation. The fraction of these objects can be as high as 20%. In particular, the flux in [OIII] line turns to be lower in two nearby edge-on spiral galaxies, which can be explained by the extinction in their galactic disks.

astro-ph↗

arXiv2007

The double Compton emissivity in a mildly relativistic thermal plasma within the soft photon limit

We provide simple and accurate analytic approximations for the low frequency double Compton emission coefficient that are applicable in a broad range of physical situations up to mildly relativistic temperatures. These approximations may be useful for checking in which circumstances the double Compton process is important. We perform series expansions of the double Compton emission integral for low energies of the incident photon and electron and compare the derived analytic expressions with the results obtained by numerical integrations of the full double Compton cross section. We explicitly derived analytic approximations to the low frequency double Compton emission coefficient for initial monochromatic photons and Wien spectra. We show that combining the analytic approximations given in this paper, an accuracy of better than 5% over a very broad range of temperatures and under various physical conditions can be achieved. The double Compton emissivity strongly depends on the ratio of the incoming photon and electron energies: for hard photons and cold electrons the emission is strongly suppressed compared to the case of similar photon and electron energy, whereas in the opposite situation, i.e. hot electrons and soft initial photons, the emission is enhanced. For photons and electrons close to thermodynamic equilibrium the double Compton emissivity increases less rapidly with temperature than in the Lightman-Thorne approximation and the corrections exceed ~10% for temperatures above 4 keV.

astro-ph↗

arXiv2005

A hard X-ray survey of the Crux Galactic spiral arm tangent. A catalog of sources

This work is part of a large solid angle hard X-ray survey. We analized a number of observations by the IBIS telescope aboard the INTEGRAL observatory covering the Crux Galactic spiral arm tangent. We have detected 46 hard X-ray sources, with 15 of them being new. Among the identified sources there are 12 AGNs, 11 HMXBs, 6 LMXBs and 2 active stars. 13 sources remain unidendified.

astro-ph↗

arXiv2004

Radiative feedback from quasars and the growth of massive black holes in stellar spheroids

We discuss the importance of feedback via photoionization and Compton heating on the co-evolution of massive black holes (MBHs) at the center of spheroidal galaxies and their stellar and gaseous components. We first assess the energetics of the radiative feedback from a typical quasar on the ambient interstellar medium. We then demonstrate that the observed Mbh-sigma relation could be established following the conversion of most of the gas of an elliptical progenitor into stars, specifically when the gas-to-stars mass ratio in the central regions has dropped to a low level ~0.01 or less, so that gas cooling is no longer able to keep up with the radiative heating by the growing central MBH. A considerable amount of the remaining gas will be expelled and both MBH accretion and star formation will proceed at significantly reduced rates thereafter, in agreement with observations of present day ellipticals. We find further support for this scenario by evolving over an equivalent Hubble time a simple, physically based toy model that additionally takes into account the mass and energy return for the spheroid evolving stellar population, a physical ingredient often neglected in similar approaches.

astro-ph↗

arXiv2004

Radiative Feedback from Quasars and the Growth of Supermassive Black Holes

We discuss the role of feedback via photoionization and Compton heating in the co-evolution of massive black holes at the center of spheroidal galaxies and their stellar and gaseous components. We first assess the energetics of the radiative feedback from a typical quasar on the ambient interstellar gas. We then demonstrate that the observed Mbh-sigma relation could be established at a relatively early epoch in galactic evolution when the formation of the stellar bulge was almost completed and the gas-to-stars mass ratio was reduced to a low level ~0.01 such that cooling could not keep up with radiative heating. A considerable amount of gas was expelled at that time and black hole accretion proceeded at a much lower rate thereafter.

astro-ph↗

arXiv2004

A physically motivated toy model for the BH-spheroid coevolution

We present a summary of the results obtained with a time-dependent, one-zone toy model aimed at exploring the importance of radiative feedback on the co-evolution of massive black holes (MBHs) at the center of stellar spheroids and their stellar and gaseous components. We consider cosmological infall of gas as well as the mass and energy return for the evolving stellar population. The AGN radiative heating and cooling are described by assuming photoionization equilibrium of a plasma interacting with the average quasar SED. Our results nicely support a new scenario in which the AGN accretion phase characterized by a very short duty-cycle (and now common in the Universe) is due to radiative feedback. The establishment of this phase is recorded as a fossil in the Magorrian and Mbh-sigma relations.

astro-ph↗

arXiv2004

Hard X-ray view of the past activity of Sgr A* in a natural Compton mirror

We report the association of the recently discovered hard X-ray source IGR J17475-2822 with the giant molecular cloud Sgr B2 in the Galactic Center region. The broad band (3-200 keV) spectrum of the source constructed from data of different observatories strongly supports the idea that the X-ray emission of Sgr B2 is Compton scattered and reprocessed radiation emitted in the past by the Sgr A* source. We conclude that 300-400 years ago Sgr A* was a low luminosity (L ~ 1.5e39 erg/s at 2-200 keV) AGN with a characteristic hard X-ray spectrum (photon index Gamma ~ 1.8). We estimate the mass and iron abundance of the Sgr B2 scattering gas at 2e6 Msun (r/10pc)^2 and 1.9 solar, respectively (where r is the radius of the cloud).

astro-ph↗

arXiv2003

Quasars: the characteristic spectrum and the induced radiative heating

Using information on the cosmic X-ray background and the cumulative light of active galactic nuclei at infrared wavelengths, the estimated local mass density of galactic massive black holes (MBHs) and published AGN composite spectra in the optical, UV and X-ray, we compute the characteristic angular-integrated, broad-band spectral energy distribution of the average quasar in the universe. We demonstrate that the radiation from such sources can photoionize and Compton heat the plasma surrounding them up to an equilibrium Compton temperature (Tc) of 2x10^7 K. It is shown that circumnuclear obscuration cannot significantly affect the net gas Compton heating and cooling rates, so that the above Tc value is approximately characteristic of both obscured and unobscured quasars. This temperature is above typical gas temperatures in elliptical galaxies and just above the virial temperatures of giant ellipticals. The general results of this work can be used for accurate calculations of the feedback effect of MBHs on both their immediate environs and the more distant interstellar medium of their host galaxies.

astro-ph↗

arXiv1999

GRANAT/SIGMA Observation of the Early Afterglow from GRB 920723 in Soft Gamma-Rays

We present a GRANAT/SIGMA observation of the soft gamma-ray afterglow immediately after GRB 920723. The main burst is very bright. After ~6 s, the burst light curve makes a smooth transition into an afterglow where flux decays as t^{-0.7}. The power-law decay lasts for at least 1000 s; beyond this time, the afterglow emission is lost in the background fluctuations. At least ~20% of main burst energy is emitted in the afterglow. At approximately ~6 s after the trigger, we also observe an abrupt change in the burst spectrum. At t<6 s, the ratio of 8-20 and 75-200 keV fluxes corresponds to the power law spectral index α=0.0-0.3. At t=6 s, the value of αincreases to α= ~1 and stays at this level afterwards. The observed afterglow characteristics are discussed in connection with the relativistic fireball model of gamma-ray bursts.

astro-ph↗

arXiv1998

The Correlation of Gamma-Ray Bursts with Active Galactic Nuclei

We search for angular correlation of gamma-ray bursts with cataloged quasars, BL Lac objects, and AGN using a large sample of relatively well-localized bursts detected by WATCH on board GRANAT and EURECA, IPN, and BATSE (327 bursts total). A statistically significant (99.99% confidence) correlation between GRB and M_B<-21 AGN in the redshift range 0.1<z<0.32 is found. The correlation with AGN is detected, with a lower significance, in three independent GRB datasets. The correlation amplitude implies that, depending on the AGN catalog completeness, 10% to 100% of bursts with peak fluxes in the range 3-30x10**-6 erg/s/cm^2 in the 100-500 keV band are physically related to AGN. The established distance scale corresponds to the energy release of order 10**52 ergs per burst.

astro-ph↗