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A. M. Cherepashchuk

Publications and source records attributed to A. M. Cherepashchuk.

48 records · Page 3Linked to original sources

Possibilities of analysis of brightness distributions for components of eclipsing variables from data of space photometry

We carried out numerical experiments on the evaluation of the possibilities of obtaining the information about brightness distributions for the components of eclipsing variables from the data of high-precision photometry expected for planned satellites COROT and Kepler. We examined a simple model of the eclipsing binary with the spherical components on circular orbits and the linear law of the limb darkening. The solutions of light curves have been obtained as by fitting of the nonlinear model, into the number of parameters of which included the limb darkening coefficients, so also by the solution of the ill-posed inverse problem of restoration of brightness distributions across the disks of stars without rigid model constraints on the form of these functions. The obtained estimations show that if the observational accuracy amounts to 0.0001 then the limb darkening coefficients can be found with the relative error approximately 0.01 . The brightness distributions across the disks of components can be restored also nearly with the same accuracy.

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Searches for Black Holes. the Most Recent Results

Black holes were predicted by Einstein General Relativity (GR). Because of unusual properties of these objects their existence is almost unbelievable. There are gravitation theories which do not predict the black hole appearance. By now, astronomers discovered a few hundreds of massive and highly compact objects with observational features which are very similar to the properties of black holes predicted by GR. To confirm existence of black holes in the Universe, a number of groundbased and space experiments are planned to be held in the coming decade.

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INTEGRAL observations of SS433: Results of coordinated campaign

Results of simultaneous INTEGRAL and optical observations of galactic microquasar SS433 in May 2003 and INTEGRAL/RXTE observations in March 2004 are presented. Persistent precessional variability with a maximum to minimum uneclipsed hard X-ray flux ratio of \sim 4 is discovered. The 18-60 keV X-ray eclipse is found to be in phase with optical and near infrared eclipses. The orbital eclipse observed by INTEGRAL in May 2003 is at least two times deeper and apparently wider than in soft X-ray band. The broadband X-ray spectrum 2-100 keV simultaneously detected by RXTE/INTEGRAL in March 2004 can be described by bremsstrahlung emission from optically thin thermal plasma with kT\sim 30 keV. The optical spectroscopy with the 6-m SAO BTA telescope confirmed the optical companion to be an A5-A7 supergiant. For the first time, spectorscopic indications of a strong heating effect in the optical star atmosphere are found. The measurements of absorption lines which are presumably formed in the non-illuminated side of the supergiant yield its radial velocity semi-amplitude K_v=132\pm 9 km/s. The analysis of the observed hard X-ray light curve and the eclipse duration, combined with spectroscopically found optical star radial velocity corrected for the strong heating effect, allows us to model SS433 as a massive X-ray binary. Assuming that the hard X-ray source in SS433 is eclipsed by the donor star that exactly fills its Roche lobe, the masses of the optical and compact components in SS433 are suggested to be M_v\approx 30 M_\odot and M_x\approx 9M_\odot, respectively. This provides further evidence that SS433 is a massive binary system with supercritical accretion onto a black hole.

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Super-Massive Black Holes and Dark Halos

The relations between masses of Super-Massive Black Holes, Mbh, in galactic nuclei, maximal rotational velocities, Vm, and indicative masses, Mi, of galaxies are studied for galaxies with the available rotation curves. Mbh correlates with both Vm and Mi, although much weaker than with the central velocity dispersion S0. Masses Mbh for early-type galaxies (S0-Sab), which usually possess more luminous bulges, are, on average, larger than those for late-type galaxies with similar velocities of rotation. It enables to conclude that masses of black holes are determined mainly by the bulge properties, and - much weaker - by dark haloes of galaxies.

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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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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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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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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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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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Synthetic Doppler maps of gaseous flows in IP Peg

We present synthetic Doppler maps of gaseous flows in binary IP Peg based on the results of 3D gasdynamical simulations. Using of gasdynamical calculations alongside with the Doppler tomography technique permits us to identify the main features of the flow on the Doppler maps without solution of an ill-posed inverse problem. Comparison of synthetic tomograms with observations shows that in quiescence there are two zones of high emission: a shock wave on the edge of the stream from L_1 caused by the interaction of the gas of circumbinary envelope and the stream, and the dense region in a apoastron of quasi-elliptical accretion disk. A single arm of the spiral shock and the stream itself give a minor input to the total brightness. During outburst the accretion disk dominates, and the most emitive regions are the two arms of the spiral shock.

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Wolf-Rayet stars and GRB connection

Observed properties of GRBs, WR stars and their CO-cores in the end of evolution are analyzed. A possible bimodality of the observed GRB energy distribution ($10^{48}$ erg for GRB9809425; $3\times 10^{51}÷2\times 10^{54}$ erg for others) is in accord with the bimodal mass distribution of relativistic objects ($M_{NS}=(1.35\pm 0.15) M_\odot$; $M_{BH}=(4÷15) M_\odot$). The peculiarity of SN1998bw can be related to the rotation of the collapsing CO-core. The expected galactic collapse rate of CO-cores of most compact WR stars of type WO is $\sim 10^{-5}$ per year, only by one and a half order of magnitude higher than the GRB rate. The allowance for a gamma-ray beaming or random outcome of the CO-core collapse due to some instabilities brings this rate in accordance GRB rate. We argue that WR stars (most probably, of type WO) can be considered as progenitors of cosmic gamma-ray bursts. Two types of GRBs are predicted in correspondence with the bimodal mass distribution of the relativistic objects. Three types of optical afterglows should appear depending on which CO-core is collapsing: of a single WR star, of a WR star in a WR+O or a hypothetic WR+(A-M) binary system. We briefly discuss a model of GRB as a transient phenomenon occurring at early stages of galactic evolution ($z>1$), when very massive ($M>100 M_\odot$) low-metallicity stars could form. WR-galaxies can be most probable candidates for GRB host galaxies.

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Evidence for the Absence of a Stream-Disk Shock Interaction (Hot Spot) in Semi-Detached Binary Systems. Comparison of Numerical Simulation Results and Observations

The results of three-dimensional numerical simulations of the flow of matter in non-magnetic semidetached binary systems are presented. Self-consistent solutions indicate the absence of a shock interaction between the stream of matter flowing from the inner Lagrange point and the accretion disk (a "hot spot"). At the same time, the interaction between the stream and the common envelope of the system forms an extended shock wave along the edge of the stream, whose observational properties are roughly equivalent to those of a hot spot in the disk. Comparison of synethesized and observed light curves confirm the adequacy of the proposed model for the flow of matter without formation of a hot spot. The model makes it possible for the first time to reproduce the variety of the observed light curves of cataclysmic variables in the framework of a single model, without invoking additional assumptions.

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