We have used observations from CGRO to study the variation in the MeV emission of Cygnus X-1 between its low and high X-ray states. These data provide a measurement of the spectral variability above 1 MeV. The high state MeV spectrum is found to be much harder than that of the low state MeV spectrum. In particular, the power-law emission seen at hard X-ray energies in the high state spectrum (with a photon spectral index of 2.6) is found to extend out to at least 5 MeV, with no evidence for any cutoff. Here we present the data and describe our efforts to model both the low state and high state spectra using a hybrid thermal/nonthermal model in which the emission results from the Comptonization of an electron population that consists of both a thermal and nonthermal component.
Space Science Center, Physics
AIP Conference Proceedings
Digital Object Identifier (DOI)
Gamma-ray spectral variability of Cygnus X-1 McConnell, M. L. and Bennett, K. and Bloemen, H. and Collmar, W. and Hermsen, W. and Kuiper, L. and Paciesas, W. and Phlips, B. and Poutanen, J. and Ryan, J. M. and Schönfelder, V. and Steinle, H. and Strong, A. W. and Zdziarski, A. A., AIP Conference Proceedings, 587, 96-100 (2001), DOI:http://dx.doi.org/10.1063/1.1419379
© 2001 American Institute of Physics