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Abstract: We present a study of the correlations between spectral, timing propertiesand mass accretion rate observed in X-rays from the Galactic Black Hole BHbinary GRS 1915+105 during the transition between hard and soft states. Weanalyze all transition episodes from this source observed with RXTE,coordinated with Ryle Radio Telescope RT observations. We show thatbroad-band energy spectra of GRS 1915+105 during all these spectral states canbe adequately presented by two Bulk Motion Comptonization BMC components: ahard component BMC1, photon index Gamma 1=1.7-3.0 with turnover at highenergies and soft thermal component BMC2, Gamma 2=2.7-4.2 with characteristiccolor temperature <1 keV, and the redskewed iron line LAOR component. We alsopresent observable correlations between the index and the normalization of thedisk -seed- component. The use of -seed- disk normalization, which ispresumably proportional to mass accretion rate in the disk, is crucial toestablish the index saturation effect during the transition to the soft state.We discovered the photon index saturation of the soft and hard spectralcomponents at values of 4.2 and 3 respectively. We present a physical modelwhich explains the index-seed photon normalization correlations. We argue thatthe index saturation effect of the hard component BMC1 is due to the softphoton Comptonization in the converging inflow close to BH and that of softcomponent is due to matter accumulation in the transition layer when massaccretion rate increases. In addition to our spectral model components we alsofind a strong feature of -blackbody-like- bump which color temperature is about4.5 keV in eight observations of the intermediate and soft states. We discuss apossible origin of this -blackbody-like- emission.



Author: Lev Titarchuk University of FerraraGSFCNRLGMU, Elena Seifina Moscow State University-Sternberg Astronomical Institute

Source: https://arxiv.org/







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