We present an analysis of the X-ray spectral properties observed from black hole candidate ( BHC ) binary SSÂ 433 .
We have analyzed Rossi X-ray Time Explorer ( RXTE ) data from this source , coordinated with Green Bank Interferometer/RATAN-600 .
We show that SSÂ 433 undergoes a 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 that we identify as a ” blackbody-like ( BB ) ” component which color temperature is in the range of 4-5 keV in 24 IS spectra during the radio outburst decay in SSÂ 433 .
Our observational results on the ” high temperature BB ” bump leads 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 and Titarchuk .
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 SSÂ 433 , M _ { bh } { { } _ { > } \atop { } ^ { \sim } } 2 solar masses , using the scaling method using BHC GX 339-4 as a reference source .
Our estimate of the BH mass in SS 433 is consistent with recent BH mass measurement using the radial-velocity measurements of the binary system by Hillwig & Gies who find that M _ { x } = ( 4.3 \pm 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 SSÂ 433 , like in a number of other BH candidates , is the strong observational evidence for the presence of a BH in SSÂ 433 .