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K. A. Postnov

Publications and source records attributed to K. A. Postnov.

At least 91 records · Page 5Linked to original sources
arXiv2004

Gamma-ray Bursts and Hypernovae

In these proceedings, I discuss recent progress in understanding the nature of cosmic gamma-ray bursts (GRB), with the focus on the apparent relation of several GRBs with an energetic subclass of stellar explosions, type Ib/c core-collapse supernovae. This relation provides the strong case that the GRB phenomenon is connected with the final stages of massive star evolution and possibly with the formation of neutron stars and black holes. I speculate that intrinsically faint, apparently spherically symmetric nearby GRB 980425 and 031203 associated with bright hypernovae SN 1998bw and SN 2003lw, respectively, can signal the formation of a neutron star in the end of gravitational collapse, while the bulk of cosmological GRBs with a universal energy release of $\sim 10^{51}$ ergs in narrow-collimated jets are produced when a black hole is formed. In the former case, the energy source of GRB is the neutron star rotational energy; in the latter case the GRB energy is due to non-stationary accretion onto the black hole.

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arXiv2004

On the constraining observations of the dark GRB 001109 and the properties of a z = 0.398 radio selected starburst galaxy contained in its error box

We present optical and NIR (near infrared) follow up observations of the GRB 001109 from 1 to 300 days after the burst. No transient emission was found at these wavelengths within this GRB's (Gamma Ray Burst) 50" radius BeppoSAX error box. Strong limits (3 sigma) are set with: R >~ 21, 10.2 hr after the GRB; I >~ 23, 11.4 hr after the GRB; H >~ 20.7, 9.9 hr after the GRB; and Ks >~ 20, 9.6 hours after the GRB. We discuss whether the radio source found in the GRB's error box (Taylor et al. 2000) might be related to the afterglow. We also present a multiwavelength study of a reddened starburst galaxy, found coincident with the potential radio and the X ray afterglow. We show that our strong I band upper limit makes of the GRB 001109 the darkest one localised by the BeppoSAX's NFI (Narrow Field Instrument), and it is one of the most constraining upper limits on GRB afterglows to date. Further to it, the implications of these observations in the context of dark GRBs are considered.

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arXiv2004

Coordinated INTEGRAL and optical observations of SS433

Results of simultaneous {\it INTEGRAL} and optical observations of galactic microquasar SS433 in May 2003 are presented. The analysis of the X-ray and optical eclipse duration and hard X-ray spectra obtained by {\it INTEGRAL} together with optical spectroscopy obtained on the 6-m telescope allows us to construct a model of SS433 as a massive X-ray binary. X-ray eclipse in hard X-rays has a depth of $\sim 80%$ and extended wings. The optical spectroscopy allows us to identify the optical companion as a A5-A7 supergiant and to measure its radial velocity semi-amplitude $K_v=132$ km/s. A strong heating effect in the optical star atmosphere is discovered spectroscopically. The observed broadband X-ray spectrum 2-100 keV can be described by emission from optically thin thermal plasma with $kT\sim 15-20 keV$

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arXiv2004

INTEGRAL/IBIS survey of the Sagittarius Arm Tangent region: A source catalog

Analysis of 18-120 keV images of the Sagittarius Arm Tangent region (SATR) obtained by IBIS telescope onboard INTEGTRAL observatory during the spring of 2003 is performed. In the 18-60 keV energy range, 28 sources have been detected with a flux level above 1.4 mCrab. Of these sources, 16 were identified earlier as galactic X-ray binary systems, 3 as extragalactic objects, 2 as pulsars inside supernova remnants, and 7 has unknown nature. The analysis revealed the presence of three previously unknown sources. Fourteen sources show significant flux in the 60-120 keV energy range

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arXiv2004

Earliest spectroscopy of the GRB030329 optical transient

We present the earliest BTA (SAO RAS 6-m telescope) spectroscopic observations of the GRB030329 optical transient (OT), which almost coincide in time with the first "break" (t ~ 0.5 day after the GRB) of the OT light curve. The BTA/MPFS (Multi Pupil Fiber Spectrograph) spectra are clearly not smooth: the OT spectra showed a continuum with several broad spectral features at about 4000, 4450, 5900AA. The OT spectrum showed some evolution starting from the first night after the burst, and the beginning of spectral changes are seen as early as ~10-12 hours after the GRB. The onset of the spectral changes for t < 1 day indicates that the contribution from Type Ic supernova (SN) into the OT optical flux can be detected earlier. So, summarizing our and other spectroscopic data on the OT we confirm the evolution of the OT spectrum and color pointed also by other authors (Hjorth et al. 2003; Matheson et al. 2003b). The early spectra of GRB030329/SN2003dh properties can be consistent with a shock moving into a stellar wind formed from the pre-SN. Such a behavior (similar to one near the UV shock breakout in SNe) can be explained by the existence of a dense matter in the immediate surroundings of GRB/SN progenitor.

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arXiv2004

Masses of Stellar Black Holes and Testing Theories of Gravitation

We analyze the mass distribution of stellar black holes derived from the light and radial velocity curves of optical stars in close binary systems using dynamical methods. The systematic errors inherent in this approach are discussed. These are associated primarily with uncertainties in models for the contribution from gaseous structures to the optical brightness of the systems under consideration. The mass distribution is nearly flat in the range 4-15M_sun. This is compared with the mass distribution for black holes in massive close binaries, which can be manifest as ultraluminous X-ray sources (L_x > 10^39 erg/s) observed in other galaxies. If the X-ray luminosities of these objects correspond to the Eddington limit, the black-hole mass distribution should be described by a power law, which is incompatible with the flat shape derived dynamically from observations of close binaries in our Galaxy. One possible explanation of this discrepancy is the rapid evaporation of stellar-mass black holes predicted in recent multi-dimensional models of gravity. This hypothesis can be verifed by measuring the stellar black-hole mass spectrum or finding isolated or binary black holes with masses below 3M_sun.

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arXiv2004

The origin of intergalactic thermonuclear supernovae

The population synthesis method is used to study the possibility of explaining the appreciable fraction (20^+12_15%) of the intergalactic (no-host) type Ia supernovae observed in galaxy clusters (Gal-Yam ete al. 2003) by binary whote dwarf merginngs in the cores of globular clusters. In a typical globular cluster, the number of merging double white dwarfs is fount to be smaller than 10^{-13} per year per average cluster star during the entire evolution of the cluster, which is a factor of 3 higher than in a Milky-Way-type galaxy. From 5 to 30% of the merging white dwarfs are dynamically expelled from the cluster with barycenter velocities up to 150 km/s. SN Ia explosions during the mergers of binary white dwarfs in dense star clusters may account for \sim 1% of the total rate of SN Ia in the central parts of galaxy clusters if the baryon mass fraction in such star clusters is \sim 0.3%.

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arXiv2003

Time-dependent thermal effects in GRB afterglows

Time-dependent thermal effects should accompany standard non-thermal afterglows of GRB when gamma-rays pass through inhomogeneous surroundings of the GRB site. Thermal relaxation of an optically thin plasma is calculated using time-dependent collisional ionization of the plasma ion species. X-ray emission lines are similar to those found in the fading X-ray afterglow of GRB 011211. Thermal relaxation of clouds or shells around the GRB site could also contribute to the varying late optical GRB afterglows, such as in GRB021004 and GRB030329.

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arXiv2003

INTEGRAL observations of SS433, a supercritically accreting microquasar with hard spectrum

Observations of SS433 by INTEGRAL carried out in March -- May 2003 are presented. SS433 is evidently detected on the INTEGRAL images of the corresponding sky region in the energy bands 25-50 and 50-100 keV. The precessional variability of the hard X-ray flux is clearly seen. The X-ray eclipse caused by the binary orbital motion is also detected. A possible origin of the hard continuum is briefly discussed.

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arXiv2003

Time-dependent thermal X-ray afterglows from GRBs

Time-dependent thermal X-ray spectra are calculated from physically plausible conditions around GRB. It is shown that account for time-dependent ionization processes strongly affects the observed spectra of hot rarefied plasma. These calculations may provide an alternative explanation to the observed X-ray lines of early GRBs afterglows (such as GRB 011211). Our technique will allow one to obtain independent constraints on the GRB collimation angle and on the clumpiness of circumstellar matter.

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arXiv2002

A Her X-1 Turn-On: Using the pulse profile to probe the outer edge of an accretion disk

The X-ray binary pulsar Her X-1 shows a wide variety of long and short term variabilities in the X-ray light curve. The 35 d variability of the source is interpreted as the influence of a warped, inclined, and twisted accretion disk periodically covering the line of sight to the central neutron star. In 1997 September we observed the ``turn-on'' of a 35 d cycle with the Rossi X-ray Timing Explorer (RXTE). Spectral analysis reveals that during early phases of the turn-on the overall spectrum is composed of X-rays scattered into the line of sight plus heavily absorbed X-rays. This interpretation is consistent with the variation of the pulse profile observed at the same time. The overall shape of the pulse profile is not changing, but towards earlier phases of the turn-on the pulse signature is steadily ``washed out''. This behavior can be understood as an influence of scattering and absorption due to the presence of the accretion disk rim. Using a Monte Carlo code we simulate the influence of both processes on a time variable, beamed emission characteristic, similar to the pulse profile of Her X-1. By comparing the results of the simulation with the observed profiles we determine the amount of scattered radiation, absorbed radiation, and the size of the scattering region.

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arXiv2002

Gamma-Ray Bursts and TeV quantum gravity

Limitations on the multi-dimensional TeV-scale quantum gravity model by Arkani-Hamed, Dimopoulos and Dvali (1998) and on model by Dvali, Gabadadze, Porrati (2000) are obtained from an analysis of gamma-ray bursts at cosmological distances (relativistic fireball model).

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arXiv2002

Broad-band gravitational-wave pulses from binary neutron stars in eccentric orbits

Maximum gravitational wave emission from binary stars in eccentric orbits occurs near the periastron passage. We show that for a stationary distribution of binary neutron stars in the Galaxy, several high-eccentricity systems with orbital periods in the range from tens of minutes to several days should exist that emit broad gravitational-wave pulses in the frequency range 1-100 mHz. The space interferometer LISA could register the pulsed signal from these system at a signal-to-noise ratio level $S/N>5\sqrt{5}$ in the frequency range $\sim 10^{-3}-10^{-1}$ Hz during one-year observational time. Some detection algorithms for such a signal are discussed.

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arXiv2001

Why NS and BH mass distribition is bimodal?

The observed mass distribution for the compact remnants of massive stars (neutron stars and black holes) and its relationship to possible mechanisms for the ejection of the envelopes of type II and Ib/c supernovae is analyzed. The conclusion is drawn that this distribution can be obtained only by a magneto-rotational mechanism for the supernovae with sufficiently long time of the field amplification, and a soft equation of state for neutron stars with limiting masses \sim1.5-1.6M_\odot. Some consequences of this hypothesis are discussed.

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arXiv2001

Orbital Eccentricity Effects on the Stochastic Gravitational Wave Background from Coalescing Binary Neutron Stars

Unresolved coalescing binary neutron stars in the Galaxy and beyond produce a stochastic gravitational wave background within the LISA frequency band, which can be potentially dangerous for possible detection of fundamentally more interesting relic cosmological backgrounds. Here we address the question what effects the unavoidable eccentricity of orbits of these systems should have on the properties of this backgrounds. In particularly, we examine starting from which frequency one-year observations with LISA can be secure from contamination by the noise produced by galactic binary neutron stars in eccentric orbits. We come to the conclusion that harmonics from such binaries do not contribute significantly above $\sim 10^{-3}$ Hz.

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arXiv2001

Gamma-Ray Bursts: Super-Explosions in the Universe and Related High-Energy Phenomena

The recent progress in studies of gamma-ray bursts, their afterglows, and host galaxies is discussed. The emphasis is given to high-energy phenomena associated with gamma-ray burst explosions: high-energy cosmic rays, neutrinos, gravitational waves. We also show how the relativistic fireball model for GRBs can be used to constrain modern theories of large and infinite extra-dimensions. In particular, in the frame of 5D gravity with the Standard Model localized on 3D brane (Dvali et al. 2000), the very existence of relativistic fireballs of $\sim 10^{53}$ ergs puts the lower bound on the quantum gravity scale $\sim 0.1$ eV.

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arXiv2001

Gravitational wave background from coalescing compact stars in eccentric orbits

Stochastic gravitational wave background produced by a stationary coalescing population of binary neutron stars in the Galaxy is calculated. This background is found to constitute a confusion limit within the LISA frequency band up to a limiting frequency $\NUlim{}\sim 10^{-3}$ Hz, leaving the frequency window $\sim 10^{-3}$--$10^{-2}$ Hz open for the potential detection of cosmological stochastic gravitational waves and of signals involving massive black holes out to cosmological distances.

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