A. M. Cherepashchuk

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.

MN112: a new Galactic candidate Luminous Blue Variable ?

We report the discovery of a new Galactic candidate Luminous Blue Variable (cLBV) via detection of an infrared circular nebula and follow-up spectroscopy of its central star. The nebula, MN112, is one of many dozens of circular nebulae detected at 24µm in the Spitzer Space Telescope archival data, whose morphology is similar to that of nebulae associated with known (c)LBVs and related evolved massive stars. Specifically, the core-halo morphology of MN112 bears a striking resemblance to the circumstellar nebula associated with the Galactic cLBV GAL079.29+00.46, which suggests that both nebulae might have a similar origin and that the central star of MN112 is a LBV. The spectroscopy of the central star showed that its spectrum is almost identical to that of the bona fide LBV PCygni, which also supports the LBV classification of the object. To further constrain the nature of MN112, we searched for signatures of possible high-amplitude (& 1 mag) photometric variability of the central star using archival and newly obtained photometric data covering a 45 year period. We found that the B magnitude of the star was constant ( 17.1� 0.3 mag) over this period, while in the I band the star brightened by 0.4 mag during the last 17 years. Although the non-detection of large photometric variability leads us to use the prefix ‘candidate’ in the classification of MN112, we remind that the long-term photometric stability is not unusual for genuine LBVs and that the brightness of PCygni remains relatively stable during the last three centuries.

Monte Carlo simulations of the broad-band X-ray continuum of SS433

We develop a Monte Carlo technique based on L.B. Lucys indivisible photon packets method to calculate X-ray continuum spectra of Comptonized thermal plasma in arbitrary geometry and apply it to describe the broad-band X-ray continuum of the galactic superaccreting microquasar SS433 observed by INTEGRAL. A physical model of the X-ray emitting region is proposed that includes thermal emission from the accretion disc, jets and hot corona where the photons of different origin are Comptonized. From comparison with INTEGRAL observations, we estimate physical parameters of the complex X-ray emitting region in SS433 and present model spectra for different viewing angles of the object.

The mass of the compact object in the X-ray binary her X-1/HZ her

We have obtained the first estimates of the masses of the components of the Her X-1/HZ Her X-ray binary system taking into account non-LTE effects in the formation of the Hγ absorption line: mx = 1.8 M⊙ and mv = 2.5 M⊙. These mass estimates were made in a Roche model based on the observed radial-velocity curve of the optical star, HZ Her. The masses for the X-ray pulsar and optical star obtained for an LTE model lie are mx = 0.85 ± 0.15 M⊙ and mv = 1.87 ± 0.13 M⊙. These mass estimates for the components of Her X-1/HZ Her derived from the radial-velocity curve should be considered tentative. Further mass estimates from high-precision observations of the orbital variability of the absorption profiles in a non-LTE model for the atmosphere of the optical component should be made.

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 mass of the compact object in the low-mass X-ray binary 2S 0921-630

We interpret the observed radial-velocity curve of the optical star in the low-mass X-ray binary 2S 0921-630 using a Roche model, taking into account the X-ray heating of the optical star and screening of X-rays coming from the relativistic object by the accretion disk. Consequences of possible anisotropy of the X-ray radiation are considered. We obtain relations between the masses of the optical and compact (X-ray) components, mv and mx, for orbital inclinations i = 60°, 75°, and 90°. Including X-ray heating enabled us to reduce the compact object’s mass by ∼0.5–1 M⊙, compared to the case with no heating. Based on the K0III spectral type of the optical component (with a probable mass of mv ≃ 2.9 M⊙), we concluded that mx ≃ 2.45−2.55 M⊙ (for i = 75°−90°). If the K0III star has lost a substantial part of its mass as a result of mass exchange, as in the V404 Cyg and GRS 1905+105 systems, and its mass is mv ≃ 0.65−0.75 M⊙, the compact object’s mass is close to the standard mass of a neutron star, mx ≃ 1.4 M⊙ (for i = 75°−90°). Thus, it is probable that the X-ray source in the 2S 0921-630 binary is an accreting neutron star.

Synthetic Doppler tomograms of gas flows in the binary system IP Peg

We have synthesized Doppler tomograms of gas flows in the binary system IP Peg using the results of three-dimensional gas-dynamical computations. Gas-dynamical modeling in combination with Doppler tomography enables identification of the key elements of flows in Doppler maps without solution of an ill-posed inverse problem. A comparison of the synthetic tomograms with observations shows that, in the quiescent state of the system, the most luminous components are (1) the shock wave induced by interaction between the circumbinary envelope and the stream from the Lagrange point L1 (the “hot line”) and (2) the gas condensation at the apogee of the quasi-elliptical disk. Both the single spiral shock wave arm in the gas-dynamical solution and the stream from L1 contribute little to the luminosity. In the active state of the system, when the stream from L1 does not play an appreciable role and the disk dominates, both areas of enhanced luminosity in the observational tomograms are associated with the two arms of the spiral shock wave in the disk.

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 (

Masses of stellar black holes and testing theories of gravitation

10^{48}

Peculiar nature of hard X-ray eclipse in SS433 from INTEGRAL observations

erg for GRB9809425;