GammaRay Spectral Characteristics of Thermal and NonThermal Emission from Three Black Hol.pdf

Gamma-Ray Spectral Characteristics of Thermal and Non-Thermal Emission from Three Black Holes James C. Ling1 ⋆ and William A. Wheaton2 1 Jet Propulsion Laboratory 169-327, California Institute of Technology,4800 Oak Grove 4 Drive, Pasadena, CA 91109, USA 0 2 0 Infrared Processing and Analysis Center, California Institute of Technology, 100-22, 2 Pasadena, CA 91125, USA t c O Received 2004 July 15; accepted 2004 month day 5 Abstract Cygnus X-1 and the gamma-ray transients GRO J0422+32 and GRO 2 v J1719 − 24 displayed similar spectral properties when they underwent transitions 7 between the high and low gamma-ray (30 keV to few MeV) intensity states. When 0 these sources were in the high γ-ray intensity state (γ2, for Cygnus X-1), their 3 spectra featured two components: a Comptonized shape below 200–300 keV with 9 0 a soft power-law tail (photon index 3) that extended to ∼1 MeV or beyond. When 4 the sources were in the low-intensity state (γ0 , for Cygnus X-1), the Comptonized 0 spectral shape below 200 keVtypically vanished and the entire spectrum from 30 / h keV to ∼1 MeV can be characterized by a single power law with a relatively p harder photon index ∼ 2 − 2.7. Consequently the high- and low-intensity gamma- - ray spectra intersect, generally in the ∼400 keV - ∼1 MeV range, in contrast to o r the spectral pivoting seen previously at lower (∼10 keV) energies. The presence of t the power-law component in both the high- and low-intensity gamma-ray spectra s a strongly suggests that the non-thermal process is likely to be at work in both the : v