In previous work, we have used data from the first three years of the CGRO mission to assemble a broad-band γ-ray spectrum of the galactic black hole candidate Cygnus X-1. Contemporaneous data from the COMPTEL, OSSE and BATSE experiments on CGRO were selected on the basis of the hard X-ray flux (45–140 keV) as measured by BATSE. This provided a spectrum of Cygnus X-1 in its canonical low X-ray state (as measured at energies below 10 keV), covering the energy range from 50 keV to 5 MeV. Here we report on a comparison of this spectrum to a COMPTELOSSE spectrum collected during a high X-ray state of Cygnus X-1 (May, 1996). These data provide evidence for significant spectral variability at energies above 1 MeV. In particular, whereas the hard X-ray flux decreases during the high X-ray state, the flux at energies above 1 MeV increases, resulting in a significantly harder high energy spectrum. This behavior is consistent with the general picture of galactic black hole candidates having two distinct spectral forms at soft γ-ray energies. These data extend this picture, for the first time, to energies above 1 MeV.
Space Science Center, Physics
AIP Conference Proceedings
Digital Object Identifier (DOI)
The spectral variability of Cygnus X-1 at MeV energies McConnell, M. L. and Bennett, K. and Bloemen, H. and Collmar, W. and Hermsen, W. and Kuiper, L. and Phlips, B. and Ryan, J. M. and Schönfelder, V. and Steinle, H. and Strong, A. W., AIP Conference Proceedings, 510, 114-118 (2000), DOI:http://dx.doi.org/10.1063/1.1303185
© 2000 American Institute of Physics