G. L. Case, S. Baldridge, M. L. Cherry, A. Camero-Arranz, M. Finger, P. Jenke, C. A. Wilson-Hodge, V. Chaplin
Cygnus X-1 is a high-mass x-ray binary with a black hole compact object. It
is normally extremely bright in hard x-rays and low energy gamma rays and
resides in the canonical hard spectral state. Recently, however, Cyg X-1 made a
transition to the canonical soft state, with a rise in the soft x-ray flux and
a decrease in the flux in the hard x-ray and low energy gamma-ray energy bands.
We have been using the Gamma-Ray Burst Monitor on Fermi to monitor the fluxes
of a number of sources in the 8--1000 keV energy range, including Cyg X-1. We
present light curves of Cyg X-1 showing the flux decrease in hard x-ray and low
energy gamma-ray energy bands during the state transition as well as the
several long flares observed in these higher energies during the soft state. We
also present preliminary spectra from GBM for the pre-transition state, showing
the spectral evolution to the soft state, and the post-transition state.
View original:
http://arxiv.org/abs/1111.0686
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