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Session 16 - Studies of Black Holes & Future Survey Missions.
Oral session, Monday, June 09
North Main Hall A,

[16.01] Gamma Ray Spectral Classes of Galactic Black Holes

J. E. Grove, R. A. Kroeger, J. G. Skibo (NRL), K. McNaron-Brown (GMU)

OSSE has observed more than 10 transient and persistent galactic black hole candidates. Two gamma-ray spectral classes are readily apparent and are the extensions of the X-ray low (hard) and high (soft) states. The X-ray low (hard) state extends into the low-energy gamma rays with an exponential cutoff \sim100 keV. The spectral shape is consistent with thermal Comptonization. The majority of the luminosity in this state is carried by photons above 30 keV. The X-ray high (soft) extends as a fairly soft power law (photon number index >2) with no evidence for a cutoff at energies above 500 keV, in some cases. In this state, the ultrasoft X-ray excess contains the bulk of the luminosity.

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