BATSE Earth Occultation Observations of Cygnus X-1 in 1993

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Session 67 -- Compact Objects/Stellar Winds
Oral presentation, Thursday, 2, 1994, 10:00-11:30

[67.03] BATSE Earth Occultation Observations of Cygnus X-1 in 1993

J. C. Ling, Wm. A. Wheaton, R. T. Skelton (Jet Propulsion Laboratory, California Institute of Technology), B. A. Harmon, B. C. Rubin, G. J. Fishman (NASA/Marshall Space Flight Center), W. S. Paciesas (University of Alabama in Huntsville )

We present preliminary results of approximately 250 days of BATSE Earth-occultation observation of the 20 keV to 1.8 MeV gamma-ray emission of Cygnus X-1 between April and December of 1993. Cygnus X-1 underwent several transitions in this period. The 45-140 keV flux first decreased from near the normal $\gamma_2$ level to $\gamma_1$ around the middle of May. The recovery to $\gamma_2$ took nearly two months followed by a second transition to $\gamma_1$ in early October. The flux then remained near the $\gamma_1$ level until early December, before decreasing by nearly a factor of 2 by the end of December to the lowest level, which has only rarely been seen previously. Details of these flux changes and corresponding spectral changes will be presented. We will also report results of a search for episodes of emission above $\sim 1$ MeV, as have been reported by several previous investigators.

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