ИСТИНА

We present an analysis of the X-ray spectral properties observed from black hole candidate (BHC) binary SS 433. We have analyzed Rossi X-ray Time Explorer (RXTE) data from this source, coordinated with Green Bank Interferometer/RATAN-600. We show that SS 433 undergoes an X-ray spectral transition from the low hard state (LHS) to the intermediate state (IS). We show that the X-ray broad-band energy spectra during all spectral states are well fit by a sum of so called "Bulk Motion Comptonization (BMC) component" and by two (broad and narrow) Gaussians for the continuum and line emissions respectively. In addition to these spectral model components we also find a strong feature of "blackbody-like (BB)" bump which color temperature is in the range of 4-5 keV in 24 IS spectra during the radio outburst decay in SS 433. It is worth noting that recent Monte Carlo simulations of the emergent spectra of BH sources by Laurent and Titarchuk demonstrate that the 511-keV an annihilation line is formed in the converging flow. This line emission can be seen by an Earth observer as a redshifted and broadened BB-like feature of color temperature of about 4-5 keV. Our observational results on the "high temperature BB" bump leads us to postulate the presence of gravitationally redshifted annihilation line emission in this source. We have also established the photon index saturation at about 2.3 in index vs mass accretion correlation. This index-mass accretion correlation allows us to evaluate the low limit of black hole (BH) mass of compact object in SS 433, M_bh > 2 solar masses, using the scaling method using BHC GX 339-4 as a reference source. Our estimate of BH mass in SS 433 is consistent with the recent BH mass measurement using the radial-velocity measurements of the binary system by Hillwig & Gies who find that Mx = (4.3+/-0.8) solar masses. This is the smallest BH mass found up to now among all BH sources. Moreover, the index saturation effect versus mass accretion rate revealed in SS 433, like in a number of other BHCs, is the strong observational evidence for the presence of a BH in SS 433.