V. M. Lipunov

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

Using Monte Carlo calculations of the modern scenario for binary stellar evolution, and taking account of the spin evolution of magnetized compact stars (the scenario machine), we compute for the first time the number of 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 NSs. We demonstrate a strong dependence of the binary pulsar population fractions relative to single pulsars on the mean kick velocity, and find an optimal kick velocity of 150-200 km S-l. We also investigate the way in which the merging rates of relativistic binary stars (NS + NS, NS + BH, BH + BH) depend on the kick velocity. We show that the BH + BH merging may occur, depending on the parameters of BH formation, at a rate of one per 200000-500000 yr in a Milky Way-type galaxy. The NS + NS merging rate Rns is found to be 1 per 3000 yr for zero recoil, and decreases to one per 10 000 yr even for the highest kick velocities of 400 km S-l. That the merging rates derived from evolutionary calculations are higher, by two orders of magnitude, than those based on binary pulsar statistics only, is suggested to be the result of the fact that the observable binary pulsars in pairs with NSs form only a fraction of the total number of binary NS systems. The merging rates obtained imply an expected detection rate of binary BHs (by a gravitational wave detector) comparable with and even higher than the binary NS merging rate for a wide range of parameters. Detecting the final frequency of a merging event at about 100 Hz and the shaping of the waveforms would bring firm evidence of the existence of BHs in nature.

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 Rns 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⊙), the rates obtained imply that the expected detection rate of binary BH by a LIGOtype gravitational wave detector is 10-100 times higher than the binary NS merging rate for a wide range of parameters.

Evolution of close binaries and gamma-ray bursts

We analyze the late stages of evolution of massive (M0 ≳ 8 M⊙) close binaries, from the point of view of possible mechanisms for the generation of gamma-ray bursts. It is assumed that a gamma-ray burst requires the formation of a massive (∼1 M⊙), compact (R ≲ 10 km) accretion disk around a Kerr black hole or neutron star. Such Kerr black holes are produced by core collapses of Wolf-Rayet stars in very close binaries, as well as by mergers of neutron stars and black holes or two neutron stars in binaries. The required accretion disks can also form around neutron stars that were formed via the collapse of ONeMg white dwarfs. We estimate the Galactic rate of events resulting in the formation of rapidly rotating relativistic objects. The computations were carried out using the “Scenario Machine.”We analyze here late evolutionary stages of massive (with initial mass higher than 8 masses of the Sun) close binary stars. Our purposes are to study possible mechanisms of gamma ray bursts (GRBs) origin. We suppose in this paper that GRB phenomenon require formation of massive (approx. 1 M_sun) compact (approx. 10 km) accretion disks around Kerr black holes and neutron stars. Such Kerr black holes are products of collapse of Wolf-Rayet stars in extremely close binaries and merging of neutron stars with black holes and neutron stars with neutron stars in close binary systems. Required accretion disks also can be formed around neutron stars which were formed during collapse of accreting oxygen-neon white dwarfs. We have estimated frequencies of events which lead to a rotational collapse concerned with formation of rapidly rotating relativistic objects in the Galaxy. We made our calculations using the Scenario Machine.

MASTER: The Mobile Astronomical System of Telescope-Robots.

We present the first russian robot-telescope designed to mak e prompt observations of gamma-ray bursts (http://observ.pereplet.ru). The telescopes are near Mos cow. The system of telescopes with prompt pointing rates connects to the internet. The main parameters are the following: Richter-Slefogt system telescope (355 mm, f/d=2.4); Richter-Slefogt system telescope (200mm, f/d=2.4); Flugge system telescope (280mm, f/d=2.5); TV-camera with 20x40 degree objective; Two CCD cameras (Pictor 416); One CCD Apogee Camera AP16E. Th e type of mount is German with 8 grad/sec slew rate. MASTER images stars down to 19 magnitude in a 1 min exposure covering 6 square degrees.

Gamma-ray bursts as standard-energy explosions

We show that the distribution of observed energies of GRB with known redshifts can be explained by the hypothesis of the standard energy release E0 = 5×10 51 ergs. Two situations are possible, either the beaming angle differs from burst to burst, or there is a universal emssion diagram in each burst, the observed difference being due to different viewing angles.The distribution of observed energies for gamma-ray bursts with known redshifts can be explained as a consequence of events releasing a standard energy of E0=5×1051 erg. Two situations are possible: the degree of collimation could vary from burst to burst, or there could be a universal radiation pattern for all bursts, with the observed differences being due to differences in the orientation of this pattern relative to the line of sight to the Earth.

The mechanism of supernova Ia explosion in elliptical galaxies

Abstract Recent observational data on the type Ia supernova rates are in excellent agreement with the earlier results of the population synthesis of binary stars and confirm that the overwhelming majority of type Ia supernovas (∼99%) in elliptical galaxies form via mergers of binary white dwarfs with a total mass exceeding the Chandrasekhar limit.

Optical observations of gamma-ray bursts, the discovery of supernovae 2005bv, 2005ee, and 2006ak, and searches for transients using the “MASTER” robotic telescope

We present the results of observations obtained using the MASTER robotic telescope in 2005–2006, including the earliest observations of the optical emission of the gamma-ray bursts GRB 050824 and GRB 060926. Together with later observations, these data yield the brightness-variation law t−0.55±0.05 for GRB 050824. An optical flare was detected in GRB 060926—a brightness enhancement that repeated the behavior observed in the X-ray variations. The spectrum of GRB 060926 is found to be FE ∼ E−β, where β = 1.0 ± 0.2. Limits on the optical brightnesses of 26 gamma-ray bursts have been derived, 9 of these for the first time. Data for more than 90% of the accessible sky down to 19m were taken and reduced in real time during the survey. A database has been composed based on these data. Limits have been placed on the rate of optical flares that are not associated with detected gamma-ray bursts, and on the opening angle for the beams of gamma-ray bursts. Three new supernovae have been discovered: SN 2005bv (type Ia)—the first to be discovered on Russian territory, SN 2005ee—one of the most powerful type II supernovae known, and SN 2006ak (type Ia). We have obtained an image of SN 2006X during the growth stage and a light curve that fully describes the brightness maximum and exponential decay. A new method for searching for optical transients of gamma-ray bursts detected using triangulation from various spacecraft is proposed and tested.

How abundant is the population of binary radio pulsars with black holes

Using ”Scenario Machine” we have carried out population synthesis of radio pulsar with black hole binaries (BH+Psr) in context of the most wide assumptions about star mass loss during evolution, binary stars mass ratio distribution, kick velocity and envelope mass lost during collapse. Our purpose is to display that under any suppositional parameters of evolution scenario BH+Psr population have to be abundant in Galaxy. It is shown that in the all models including models evolved by Heger et al. (2002), Woosley et al. (2002), Heger et al. (2003) expected number of the black holes paired with radio pulsars is sufficient enough to discover such systems within the next few years.

Transient Detections and Other Real-Time Data Processing from MASTER-VWF Wide-Field Cameras

Construction of robotic observatories has developed into an important and thriving field of astronomy. Their large field of view combined with the capability to be pointed at any direction makes robotic astronomical systems indispensable for tasks involving searches for transients like GRB, supernovae explosions, novae, and so forth, where both the time and direction of the search are impossible to predict. This paper describes prompt GRB observations made with MASTER-VWF wide-field cameras and the methods of image analysis and classification of transients used for real-time data processing. During seven months of operation six synchronous observations of gamma-ray bursts have been made using MASTER VWF facilities deployed in Kislovodsk and Irkutsk. In all cases high upper limits have been obtained.

“Pure” supernovae and accelerated expansion of the Universe

A special class of type Ia supernovae that is not subject to ordinary and additional intragalactic gray absorption and chemical evolution has been identified. Analysis of the Hubble diagrams constructed for these supernovae confirms the accelerated expansion of the Universe irrespective of the chemical evolution and possible gray absorption in galaxies.