On the nature of the compact object in SS433: observational evidence of X-ray photon index saturationстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:We present an analysis of theX-ray spectral properties observed from the black hole candidate (BHC) binary SS433. We have analyzed Rossi X-ray Timing Explorer 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 to the intermediate state (IS). We showthat theX-ray broadband energy spectra during all spectral states are well fitted by a sum of the socalled 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 that
we identify as a “blackbody-like (BB)” component in which the color temperature is in the range of 4–5 keV in 24 IS spectra during the radio outburst decay in SS 433. Our observational results on the “high-temperature BB” bump lead us to suggest the presence of gravitationally redshifted annihilation line emission in this source. In fact, this
spectral feature has been recently reproduced in Monte Carlo simulations by Laurent & Titarchuk. We have also established the photon index saturation at about 2.3 in index versus mass accretion correlation. This index–mass
accretion correlation allows us to evaluate the low limit of the black hole (BH) mass of the compact object in SS433, Mbh>=2 solar masses, using the scaling method using BHC GX339−4 as a reference source. Our estimate of the
BH mass in SS433 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 SS433, as in a number of other BH candidates, is strong observational evidence for the presence of a BH in SS433.