Broadband Studies of BHCs in the High, Soft State

J.E. Grove

W. Cui

Y. Ueda


Previous work with OSSE has shown that galactic black hole candidates in the X-ray high, soft state have power-law emission above 50 keV that extends at least to energies comparable to the electron rest mass. We report on recent contemporaneous observations of the transients XTE J1550-564 and GRS 1915+105 with ASCA, RXTE, and OSSE in the high, soft state. During the OSSE observations of both objects, the emission above 50 keV was slowly declining, covering a range of a factor of three in the former case and a factor of ten in the latter. This is the first time that high sensitivity observations above 50 keV have been made of these objects over such a wide range in intensity.

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On 16 Jul 1999, 09:19.