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R. A. Sunyaev

Publications and source records attributed to R. A. Sunyaev.

At least 91 records · Page 5Linked to original sources
arXiv2007

Width of X-ray lines in cooling flows

The dissipation of turbulent gas motions is one of the likely mechanisms that has been proposed to heat the intracluster medium (ICM) in the cores of clusters and groups of galaxies. We consider the impact of gas motions on the width of the most prominent X-ray emission lines. For heavy elements (like iron) the expected linewidth is much larger than the width due to pure thermal broadening and the contribution due to turbulent gas motions should be easily detected with the new generation of X-ray micro-calorimeters, such as the Spektr-RG calorimeter (SXC). For instance in the Perseus cluster the turbulent velocity required to balance radiative cooling (as derived by Rebusco et al. 2006), would imply a width of the 6.7 keV Fe line of 10-20 eV, while the pure thermal broadening is ~4 eV. The radial dependence of the linewidth is sensitive to i) the radial dependence of the velocity amplitude and ii) the "directionality" of the stochastic motions (e.g. isotropic turbulence or predominantly radial gas motions). If the width of several lines, characteristic for different gas temperatures, can be measured, then it should be possible to probe both the "directionality" and the amplitude of the gas motions. Moreover a measurement of the width would put a lower limit on the amount of the kinetic energy available for dissipation, giving a constraint on the ICM models.

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arXiv2007

Cosmological hydrogen recombination: Lyn line feedback and continuum escape

We compute the corrections to the cosmological hydrogen recombination history due to delayed feedback of Lyman-series photons and the escape in the Lyman-continuum. The former process is expected to slightly delay recombination, while the latter should allow the medium to recombine a bit faster. It is shown that the subsequent feedback of released Lyman-n photons on the lower lying Lyman-(n-1) transitions yields a maximal correction of DN_e/N_e 0.22% at z~ 1050. Including only Lyman-βfeedback onto the Lyman-αtransition, accounts for most of the effect. We find corrections to the cosmic microwave background TT and EE power spectra \change{with typical peak to peak amplitude |DC^{TT}_l/C^{TT}_l|~0.15% and |ΔC^{EE}_l/C^{EE}_l|~0.36% at l<~3000. The escape in the Lyman-continuum and feedback of Lyman-αphotons on the photoionization rate of the second shell lead to modifications of the ionization history which are very small (less than |DN_e/N_e|~few x 10^{-6}).

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arXiv2007

GRB070610 : A Curious Galactic Transient

GRB 070610 is a typical high-energy event with a duration of 5s.Yet within the burst localization we detect a highly unusual X-ray and optical transient, SwiftJ195509.6+261406. We see high amplitude X-ray and optical variability on very short time scales even at late times. Using near-infrared imaging assisted by a laser guide star and adaptive optics, we identified the counterpart of SwiftJ195509.6+261406. Late-time optical and near-infrared imaging constrain the spectral type of the counterpart to be fainter than a K-dwarf assuming it is of Galactic origin. It is possible that GRB 070610 and Swift J195509.6+261406 are unrelated sources. However, the absence of a typical X-ray afterglow from GRB 070610 in conjunction with the spatial and temporal coincidence of the two motivate us to suggest that the sources are related. The closest (imperfect) analog to Swift J195509.6+261406 is V4641 Sgr, an unusual black hole binary. We suggest that Swift J195509.6+261406 along with V4641 Sgr define a sub-class of stellar black hole binaries -- the fast X-ray novae. We further suggest that fast X-ray novae are associated with bursts of gamma-rays. If so, GRB 070610 defines a new class of celestial gamma-ray bursts and these bursts dominate the long-duration GRB demographics

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arXiv2007

Search for X-ray bursts in the INTEGRAL/IBIS data of 2003-2005 and discovery of the new X-ray burster IGR J17364-2711/17380-3749

All the observations performed with the IBIS telescope aboard the INTEGRAL observatory during the first 2.5 years of its in-orbit operation have been analyzed to find X-ray bursts. There were 1788 statistically confident events with a duration from 5 to 500 s revealed in time records of the 15-25 keV count rate of the IBIS/ISGRI detector, 319 of them were localized and, with one exception, identified with persistent X-ray sources. The known bursters were responsible for 215 of the localized events. One burst was detected from AXJ1754.2-2754, the source previously unknown as a burster, and another burst - from a new source. There was duality in determining its position - its name could be either IGR J17364-2711 or IGR J17380-3749. Curiously enough, the 138 bursts were detected from one X-ray burster - GX 354-0.

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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.

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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

On the Influence of Resonant Scattering on Cosmic Microwave Background Polarisation Anisotropies

We implement the theory of resonant scattering in the context of Cosmic Microwave Background (CMB) polarisation anisotropies. We compute the changes in the E-mode polarisation (EE) and Temperature E-mode (TE) CMB power spectra introduced by the scattering on a resonant transition with a given optical depth $τ_X$ and polarisation coefficient $E_1$. The latter parameter, accounting for how anisotropic the scattering is, depends on the exchange of angular momentum in the transition and enables, {\it a priori}, to distinguish among different possible resonances. We use this formalism in two different scenarios: cosmological recombination and cosmological reionisation. In the context of cosmological recombination, we compute predictions in frequency and multipole space for the change in the TE and EE power spectra introduced by scattering on the $H_α$ and $P_α$ lines of Hydrogen. This constitutes a fundamental test for the standard model of recombination, and the sensitivity it requires is comparable to that needed in measuring the primordial CMB B-mode polarisation component. In the context of reionisation, we study the scattering off metals and ions produced by the first stars, and find that polarisation anisotropies, apart from providing a consistency test for intensity measurements, give some insight on how reionisation evolved: since they keep memory of how anisotropic the line scattering is, they should be able to discern the OI 63.2$μ$m transition from other possible transitions associated to OIII, NII, NIII, etc. The amplitude of these signals are, however, between 10 to 100 times below the (already challenging) level of CMB B-mode polarisation anisotropies.

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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

Cosmological hydrogen recombination: populations of the high level sub-states

We present results for the spectral distortions of the Cosmic Microwave Background (CMB) arising due to bound-bound transitions during the epoch of cosmological hydrogen recombination at frequencies down to nu~100MHz. We extend our previous treatment of the recombination problem now including the main collisional processes and following the evolution of all the hydrogen angular momentum sub-states for up to 100 shells. We show that, due to the low baryon density of the Universe, even within the highest considered shell full statistical equilibrium (SE) is not reached and that at low frequencies the recombination spectrum is significantly different when assuming full SE for n>2. We also directly compare our results for the ionization history to the output of the Recfast code, showing that especially at low redshifts rather big differences arise. In the vicinity of the Thomson visibility function the electron fraction differs by roughly -0.6% which affects the temperature and polarization power spectra by <~1%. Furthermore we shortly discuss the influence of free-free absorption and line broadening due to electron scattering on the bound-bound recombination spectrum and the generation of CMB angular fluctuations due to scattering of photons within the high shells.

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arXiv2006

INTEGRAL Observations of SS433: Analysis of Precessional and Orbital X-ray Periodicities

Hard X-ray INT observations of SS 433 carried out during 2003-2005 years with an analysis of precessional and orbital variability is presented. The width of X-ray eclipse in the 25-50 keV range at the precessional phase $ψ=0.1$ (accretion disk is open to observer) is higher than that in the Ginga 18.4-27.6 keV range. This fact suggests existance the presence of hot extended corona around the supercritical accretion disk. Spectrum of hard X-rays in the range 10-200 keV does not change with the precessional phase which also suggests that hard X-ray flux is generated in the hot extended corona around the accretion disk. The parameters of this hot corona are: kT=23-25 keV, τ= 1.8-2.8. Mass ratio estimated from the analysis of the ingress part of the eclipse light curve is in the range q=m_x/m_v=0.3-0.5.

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arXiv2006

Hydrogen-like nitrogen radio line from hot interstellar and warm-hot intergalactic gas

Hyperfine structure lines of highly-charged ions may open a new window in observations of hot rarefied astrophysical plasmas. In this paper we discuss spectral lines of isotopes and ions abundant at temperatures 10^5-10^7 K, characteristic for warm-hot intergalactic medium, hot interstellar medium, starburst galaxies, their superwinds and young supernova remnants. Observations of these lines will allow to study bulk and turbulent motions of the observed target and will broaden the information about the gas ionization state, chemical and isotopic composition. The most prospective is the line of the major nitrogen isotope having wavelength 5.65 mm (Sunyaev and Churazov 1084). Wavelength of this line is well-suited for observation of objects at z=0.15-0.6 when it is redshifted to 6.5-9 mm spectral band widely-used in ground-based radio observations, and, for example, for z>=1.3, when the line can be observed in 1.3 cm band and at lower frequencies. Modern and future radio telescopes and interferometers are able to observe the absorption by 14-N VII in the warm-hot intergalactic medium at redshifts above z=0.15 in spectra of brightest mm-band sources. Sub-millimeter emission lines of several most abundant isotopes having hyperfine splitting might also be detected in spectra of young supernova remnants.

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arXiv2006

Free-bound emission from cosmological hydrogen recombination

In this paper we compute the emission coming from the direct recombination of free electrons to a given shell (n>=2) during the epoch of cosmological hydrogen recombination. This contribution leads to a total of one photon per recombined hydrogen atom and therefore a ~30-88% increase of the recombination spectrum within the frequency range 1 GHz<=nu<=100 GHz. In particular the Balmer-continuum emission increases the distortion at nu~ 690 GHz by ~92%. With our 100 shell calculations for the hydrogen atom we find that a total of ~5 photons per hydrogen atom are emitted when including all the bound-bound transitions, the 2s two-photon decay channel and the optically thin free-bound transitions. Since the direct recombination continuum at high n is very broad only a few n-series continuua are distinguishable and most of this additional emission below nu<~30 GHz is completely featureless.

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arXiv2006

Lines in the Cosmic Microwave Background Spectrum from the Epoch of Cosmological Hydrogen Recombination

We compute the spectral distortions of the Cosmic Microwave Background (CMB) arising during the epoch of cosmological hydrogen recombination within the standard cosmological (concordance) model for frequencies in the range 1 GHz-3500 GHz. We follow the evolution of the populations of the hydrogen levels including states up to principle quantum number $n=30$ in the redshift range $500\leq z\leq 3500$. All angular momentum sub-states are treated individually, resulting in a total number of 465 hydrogen levels. The evolution of the matter temperature and the fraction of electrons coming from HeII are also included. We present a detailed discussion of the distortions arising from the main dipolar transitions, e.g. Lyman and Balmer series, as well as the emission due to the two-photon decay of the hydrogen 2s level. Furthermore, we investigate the robusteness of the results against changes in the number of shells considered. The resulting spectral distortions have a characteristic oscillatory behaviour, which might allow experimentalists to separate them from other backgrounds. The relative distortion of the spectrum exceeds a value of $10^{-7}$ at wavelengths longer than 21cm. Our results also show the importance of detailed follow-up of the angular momentum sub-states, and their effect on the amplitude of the lines. The effect on the residual electron fraction is only moderate, and mainly occurs at low redshifts. The CMB angular power spectrum is changed by less than 1%. Finally, our computations show that if the primordial radiation field is described by a pure blackbody, then there is no significant emission from any hydrogen transition at redshifts greater than $z \sim 2000$. This is in contrast to some earlier works, where the existence of a `pre-recombination' peak was claimed.

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arXiv2006

Hard X-ray Bursts Detected by the IBIS Telescope Onboard the INTEGRAL Observatory in 2003-2004

All of the observations performed with the IBIS telescope onboard the INTEGRAL observatory during the first one and a half years of its in-orbit operation (from February 10, 2003, through July 2, 2004) have been analyzed to find X-ray bursts. IBIS/ISGRI detector lightcurves total count rate in the energy range 15-25 keV revealed 1077 bursts of durations from ~5 to ~500 s detected with a high statistical significance (only one event over the entire period of observations could be detected by a chance with a probability of 20%). Apart from the events associated with cosmic gamma-ray bursts (detected in the field of view or passed through the IBIS shield), solar flares, and activity of the soft gamma repeater SGR1806-20, we were able to localize 105 bursts and, with one exception, to identify them with previously known persistent or transient X-ray sources (96 were identified with known X-ray bursters). In one case, the burst source was a new burster in a low state. We named it IGR J17364-2711. Basic parameters of the localized bursts and their identifications are presented in the catalog of bursts. Curiously enough, 61 bursts were detected from one X-ray burster - GX 354-0. The statistical distributions of bursts in duration, maximum flux, and recurrence time have been analyzed for this source. Some of the bursts observed with the IBIS/ISGRI telescope were also detected by the JEM-X telescope onboard the INTEGRAL observatory in the standard X-ray energy range 3-20 keV.

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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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arXiv2006

XSS J00564+4548 and IGR J00234+6141 -- new cataclysmic variables from RXTE and INTEGRAL all sky surveys

We present the results of optical identification of two X-ray sources from RXTE and INTEGRAL all sky surveys: XSS J00564+4548 and IGR J00234+6141. Using the optical data from Russian-Turkish 1.5-m Telescope (RTT150) and SWIFT X-ray observations, we show that these sources most probably are intermediate polars, i.e. binary systems with accreting white dwarfs with not very strong magnetic field (<~10 MG). Periodical oscillations of optical emission with periods 480 s and 570 s were found. We argue that these periods most probably correspond to the rotating periods of the white dwarfs in these systems. Further optical observations scheduled at RTT150 will allow to study the parameters of these systems in more detail.

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arXiv2006

Accretion of helium and metal-rich gas onto neutron stars and black holes at high luminosities

Ultraluminous X-ray sources fed by Wolf-Rayet star winds and X-ray bursters in ultracompact binaries with He or C white dwarfs have accretion disks, whose properties may significantly differ from those of pure H alpha-accretion disks. We have therefore included the dependence on charge number Z and mean molecular weights mu_{e/I} into the Shakura and Sunyaev (1973) scaling relations for the key parameters of the disk. Furthermore, we also consider the case of the pseudo-Newtonian potential of Paczynsky and Wiita (1980). These scaling relations might become useful, e.g., when estimating the illumination efficiency of the external parts of the disk. We also address the changes in the structure of the boundary (spreading) layer on the surface of neutron stars, occurring in the case of H depleted accretion disks.

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