I. E. Panchenko

Evolution of Supernova Explosion Rates in the Universe

The prospects of detecting extragalactic supernovae (SNs) down to visual magnitudes 23-25 give us hope for observing them in the most distant parts of the universe. Using a Monte Carlo method of stellar population synthesis (the Scenario Machine), we compute, under standard assumptions of stellar evolution, the rates of SNs of various types in a model galaxy and evaluate the SN rates in the universe. The expected cumulative distribution log N - m (number of events - stellar magnitude) is calculated for various SN types and different star formation histories in the universe. The results are also presented in terms of evolution of supernova units with redshifts. Recent observational data on the high-redshift SN Ia rate are in good agreement with our predictions for the relative density of baryons contained in stars at the present time (Ω* = 0.0057).

INTEGRAL observations of SS433: Results of a coordinated campaign

Results of simultaneous INTEGRAL and optical observations of the 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 ∼ 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 the soft X-ray band. The broadband 2-100 keV X-ray spectrum simultaneously detected by RXTE/INTEGRAL in March 2004 can be explained by bremsstrahlung emission from optically thin thermal plasma with kT ∼ 30 keV. 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 on the non-illuminated side of the supergiant yield its radial velocity semi-amplitude Kv = 132 ±9 km/s. The analysis of the observed hard X-ray light curve and the eclipse duration, combined with the spectroscopically determined 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 Mv ≈ 30M⊙ and Mx ≈ 9M⊙, respectively. This provides further evidence that SS433 is a massive binary system with supercritical accretion onto a black hole.

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.

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.

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.

The radioastronomical “time machine” effect can help the solution of the gamma ray bursts mystery

Abstract The possible low-frequency radio emission from the progenitors of gamma ray bursts can experience a delay from tens of seconds to hours on the way to the observer due to the dispersion in galactic and extragalactic plasma, and thus reach the observer as a radio afterglow of the burst. This opens a unique possibility (peculiar “time machine”) of seeing what happened at that place before the catastrophe.

Cosmological rates of coalescing neutron stars and GRB

Assuming that gamma-ray bursts (GRB) originate from binary neutron star (NS) or black holes (BH) merging in distant galaxies, theoretical logN-logS distributions for gamma-ray bursts (GRB) are calculated using the compact binaries coalescence rates computed for model galaxies with different star formation histories. A flat cosmological model (Ω = 1) with different values of the cosmological constant Λ is used. The calculated source evolution predicts a 5–10 times increase of the source statistics at count rates 3–10 times lower than the existing BATSE sensitivity limit. The most important parameter in fitting the 2nd BATSE catalogue is the initial redshift of star formation, which is found to bez* = 2 — 5 depending on a poorly determined average spectral index of GRB.

Tests for coalescing binary neutron stars as cosmological origin of gamma-ray bursts

Theoretical logN-logS distributions and (V/Vmax) tests of gamma-ray bursts in the model of coalescence of neutron star (NS+NS) and/or NS+black hole (NS+BH) binaries are calculated for a flat Universe (Ω=1) with different values of the cosmological constant Λ and under various assumptions about the star formation history. The observed logN-logS distribution and value of (V/Vmax)=0.33 for 411 bursts with knownCmax/Clim from the 2d BATSE catalogue are best fitted with a model for which ΩΛ = 0.2 and primary star formation occurs at redshiftsz≃5–6.

Gravitational wave sky

Abstract A view of the sky seen in gravitational waves (GW) in a wide frequency range (∼ 10−9–103 Hz) is considered. Stochastic gravitational wave background (GWB) produced by binary systems, both galactic and extragalactic in origin, studied in more detail. Critical frequencies above which the galactic and extragalactic GWB becomes transparent for a GW detector with 1° angular resolution are about 2 × 10−3 Hz and ∼ 10 Hz, respectively. A realistic “map” of the GW sky is constructed based on realistic matter distribution within a distance of ∼ 50 Mpc according to Tullys Catalogue of Nearby Galaxies. Rates of coalescence of binary neutron stars (NS) and of supernova explosions for these galaxies are about 3 and 40 per year, respectively. The calculated rate of binary NS merging, about 10−4 per year per 1011 M[odot], yields ∼ 103 events for a LIGO limiting sensitivity hc ≃ 10−21.9 at the frequency 100 Hz.