Galactic Black Hole Binaries: High-Energy Radiation
NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
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Observations of galactic black hole candidates made by the instruments aboard the Compton GRO in the hard X-ray and gamma-ray bands have significantly enhanced our knowledge of the emission properties of these objects. Understanding these observations presents a formidable challenge to theoretical models of the accretion flow onto the compact object and of the physical mechanisms that generate high-energy radiation. Here we summarize the current state of observations and theoretical interpretation of the emission from black hole candidates above 20 keV. The all-sky monitoring capability of BATSE allows, for the first time, nearly continuous studies of the high-energy emission from more than a dozen black hole candidates. These long-term datasets are particularly well-suited to multi- wavelength comparison studies, from the radio upward in frequency Zhang et al. 1997a, these proceedings. Energy spectral evolution andor spectral state transitions have been observed from many of the black hole candidates. Moderately deep searches of the galactic plane suggest a deficit of weak gamma-ray transients. Such population studies have implications for the origin of black hole binaries and the nature of accretion events.