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M. E. Prokhorov

Publications and source records attributed to M. E. Prokhorov.

52 records · Page 3Linked to original sources
arXiv1998

Orbital evolution of a binary neutron star and gravitational radiation

We consider the dependence of the internal structure of a neutron star in a close binary system on the semi-major axis of the binary orbit, focusing on the case when the Roche lobes of the components are nearly filled. We adopt a polytropic equation of state. The temporal evolution of the semi-major axis and its dependence on the mass ratio of the binary components and the polytropic index are determined. The calculation are carried out right up to the moment of contact, when quasi-stationary model becomes invalid. We analyze differences in the shapes of the pulses of gravitational radiation emitted by a pair of point masses and by a binary neutron star, taking into account its internal structure and tidal deformations.

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arXiv1998

RXTE highlights of 34.85-day cycle of Her X-1

An analysis of the publically available RXTE archive on Her X-1 including data on 23 34.85-day cycles is performed. The turn-on times for these cycles are determined. The number of cycles with a duration of 20.5 orbits has been found exceedingly larger than of shorter (20 orbits) or longer (21 orbits). A correlation between the duration of a cycle and its mean X-ray flux is noted. The mean X-ray light curve shows a very distinct short-on state. The anomalous X-ray absorption dip is found during the first orbit after the turn-on in the main-on state for the cycles starting near the binary phase 0.25, while is present during two successive orbits in the low-on state. The post-eclipse recovery feature have not been found in the main-on state but appears at least for two orbits during the low-on state. The pre-eclipse dips are present both in main-on and low-on state and demonstrate the behaviour as in early observations. The comparison of durations of the main-on and short-on states enabled us to constrain the accretion disk semi-thickness and its inclination to the orbital plane.

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arXiv1998

Galactic Binary Gravitational Wave Noise within LISA Frequency Band

Gravitational wave noise associated with unresolved binary stars in the Galaxy is studied with the special aim of determining the upper frequency at which it stops to contribute at the rms noise level of the proposed space-born interferometer (LISA). The upper limit to this background is derived from the statistics of SN Ia explosions, part of which can be triggered by binary white dwarf coalescences. The upper limiting frequency at which binary stochastic noise crosses LISA rms sensitivity is found to lie within the range 0.03-0.07 Hz, depending on the galactic binary white dwarf coalescence rate. To be reliably detectable by LISA, the energy density of relic cosmological background per logarithmic frequency interval should be Omega_{GW}h_{100}^2>10^{-8} at f>0.03 Hz.

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arXiv1997

Evolution of close binaries after the burst of starformation for different IMFs

We use "Scenario Machine" -- the population synthesis simulator -- to calculate the evolution of populations of selected types of X-ray sources after a starformation burst with the total mass in binaries (1--1.5) \cdot 10^6 M_{\odot}$ during the first 20 Myr after a burst. We present here the results of two sets of runs of the program. In the first set we examined the following types of close binaries: transient sources-- neutron stars with Be- stars; ``X-ray pulsars''-- neutron stars in pairs with supergiants; Cyg X-1-like sources-- black holes with supergiants; ``SS443-like sources''-- superaccreting black holes. We used two values of the exponent $α$ in the initial mass function: 2.35 (Salpeter's function) and 1 (``flat spectrum''). The calculations were made for the folowing values of the upper limit of the mass function: 120 and 30 $M_{\odot}$. For the ``flat spectrum'', suggested in (Contini et al, 1995), the number of sources of all types significantly increased. With the ``flat spectrum'' and with the upper mass limit 120 $M_{\odot}$ we obtained hundreds of sources of all calculated types. Decreasing of the upper mass limit below the critical mass of a black hole formation increase the number of transient sources with neutron stars up to $\approx 300$. In the second set we examined the evolution of of 12 other types of X-ray sources for $α=1$, $α=1.35$ and $α=2.35$ and for three upper mass limits: 120 $M_{\odot}$, 60 $M_{\odot}$, 40 $M_{\odot}$ (see Perez-Olia & Colina 1995 for the reasons for such upper limits) on the same time scale 20 Myr after a star formation burst.

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arXiv1997

Distribution of the luminosity of accreting isolated compact objects

We present here the computer model of the distribution of the luminosity, produced by old isolated neutron stars and black holes accreting from the interstellar medium in the Galaxy in R-Z plane. We show, that the luminosity distributions have a torus-like structure, with the maximum at $\approx 5-6 kpc$.

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arXiv1997

An independent estimate of the cosmological distance to GRB970228 and GRB970508

Assuming binary neutron star mergings as a standard-candle model for GRBs, an independent estimate is obtained for the redshift of GRB970228 and GRB970508 with optical counterparts, using mean statistical properties of GRBs observed by BATSE. We derive z=0.7\pm 0.1 and z=1.9\pm 0.1 for GRB970228 and GRB970508 respectively, depending on the power-law index of the GRB spectrum s=-1.1\pm 0.3 and the value of the redshift of the initial star formation z_*=3-10 in a flat Ω=1 Universe with a cosmological term Λ=0.7.

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arXiv1997

Merging Rates of Compact Binaries in the Universe: Gravitational Waves and Gamma-Ray Bursts

Merging rates of compact binaries (double neutron stars or black holes) are calculated based on the modern concept of binary stellar evolution. It is found that the initial laser interferometers with an rms-sensitivity of $10^{-21}$ at the frequency 100 Hz can detect 10-700 black holes and only \sim 1 neutron star coalescences in a 1-year integration time. Implications of the evolutionary effects to the cosmological origin of GRB are also discussed.

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arXiv1997

Formation and coalescence of relativistic binary stars: effect of kick velocity

Galactic binary pulsars with different companion types (OB-star, white dwarf (WD), neutron star (NS), black hole (BH), or planet) assuming various phenomenological distributions for kick velocities of newborn NS are studied. The merging rates of relativistic binary stars (NS+NS, NS+BH, BH+BH) dependence on the kick velocity is specially adresed. The BH+BH merging is shown to occur, depending on parameters of BH formation, at a rate of one per 200,000 -- 500,000 years in a Milky Way type galaxy. The NS+NS merging rate $R_{ns}$ is found to be 1 per \sim 3,000 years for zero recoil, and decrease to one per 10,000 years even for the highest kick velocities of 400 km/s. That the merging rates derived from evolutionary calculations are by two order of magnitude higher than those based on binary pulsar statistics only, is suggested to be due to the fact that the observable binary pulsars in pairs with NS form only a fraction of the total number of binary NS systems. The expected detection rate of binary BH by a LIGO-type gravitational wave detector comparable with and even higher than the binary NS merging rate for a wide range of parameters.

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arXiv1997

Black holes and gravitational waves: simultaneous discovery by initial laser interferometers

Study of gravitational-radiation induced merging rates of relativistic binary stars (double neutron stars; neutron star + black hole; double black holes) shows that the first-generation gravitational wave interferometers with an rms-sensitivity of $10^{-21}$ at frequency 100 Hz can detect 10-700 black hole and only $\sim 1$ neutron star coalescences in a 1-year integration time in a wide range of stellar evolution parameters. It is notable that modern concepts of stellar evolution predict that the first detection of gravitational wave will independently discover black holes.

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arXiv1996

First LIGO events: binary black holes mergings

Based on evolutionary scenarios for binary stellar evolution we study the merging rates of relativistic binary stars (NS+NS, NS+BH, BH+BH) under different assumptions of BH formation. We find the BH+BH merging rate in the range one per 200,000 -- 500,000 year in a Milky-Way type galaxy, while the NS+NS merging rate $R_{ns}$ is approximately 10 times as high, which means that the expected event rate even for high mean kick velocities of NS up to 400 km/s is at least 30-50 binary NS mergings per year from within a distance of 200 Mpc. As typical BH is formed with a mass 3-10 times the NS mass (assumed 1.4 M$_\odot$), the rates obtained imply that the expected detection rate of binary BH by a LIGO-type gravitational wave detector is 10-100 times higher than the binary NS merging rate for a wide range of parameters.

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arXiv1996

Spatial distribution of accreting isolated neutron stars

We present here the computer model of the distribution of the luminosity, produced by old isolated neutron stars (OINSs) accreting from the interstellar medium (ISM). We show, that for different mean velocities of OINSs the distribution of the luminosity has a torus-like structure, with the maximum at $\approx 5 kpc$.

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arXiv1996

Binary Evolution in World Wide Web

We present a WWW-version of the {\it Scenario Machine} - a computer code designed to calculate the evolution of close binary stellar systems. The Internet users can directly access to the code and calculate binary evolutionary tracks with parameters at the user's will. The program is running on the {\it Pentium} server of the Division of the Relativistic Astrophysics of the Sternberg Astronimical Institute (http://xray.sai.msu.su/ ). The results are presented both in the form of tables and graphic diagrams. The work is always in progress. More possibilities for Internet users are intended to become available in the near future.

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arXiv1995

Population synthesis of X-ray sources at the Galactic center

We model the evolution of the selected types of X-ray sources (both with BHs and NSs) for the star formation burst at the Galactic center. For the currently assumed starburst age of 4-7 millions years, our results are consistent with the recent {\it GRANAT} X-ray observations of the Galactic center and predict a substantial number of X-ray binaries with black holes. In addition we made a very simple model of the spatial distribution of the X-ray sources, which is also consistent with the {\it GRANAT} observations. The results can be applied to other starformation regions.

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arXiv1995

Population synthesis of X-ray sources at the Galactic center

X-ray binary population at the Galactic center is proposed here to form as a result of a starburst, which is synthesized by using the ``Scenario Machine'' code of binary star evolution. For the currently assumed starburst age of 4-7 millions years, our results are consistent with the recent {\it GRANAT} X-ray observations of the Galactic center and predict a substantial number of X-ray binaries with black holes.

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arXiv1995

Evolution of the double neutron star merging rate and the cosmological origin of gamma-ray burst sources

Evolution of the coalescence rate of double neutron stars (NS) and neutron star -- black hole (BH) binaries are computed for model galaxies with different star formation rates. Assuming gamma-ray bursts (GRB) to originate from NS+NS or NS+BH merging in distant galaxies, theoretical logN--logS distributions and tests of gamma-ray bursts (GRB) are calculated for the first time taking the computed merging rates into account. We use a flat cosmological model (Omega=1) with different values of the cosmological constant Lambda and under various assumptions about the star formation history in galaxies. The calculated source evolution predicts a 5-10 times increase of the source statistics at count rates 3-10 times lower than the exising BATSE sensitivity limit. The most important parameter in fitting the 2nd BATSE catalogue is the initial redshift of star formation, which is found to be z_*=2-5 depending on a poorly determined average spectral index of GRB.

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