GBM Monitoring of Cyg X-1 During the Recent State Transitions

Details GBM Monitoring of Cyg X-1 During the Recent State Transitions GBM Monitoring of Cyg X-1 During the Recent State Transitions

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011head...12.0811c&link_type=abstract

American Astronomical Society, HEAD meeting #12, #8.11

Astronomy and Astrophysics

Astronomy

Scientific paper

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. In July 2010, however, Cyg X-1 made a transition to the 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. It remained in the soft state until April 2011 when it made the transition back to the hard state. We have been using the Gamma-Ray Burst Monitor on Fermi to monitor the fluxes of a number of sources, including Cyg X-1, in the 8-1000 keV energy range using the Earth occultation technique. We present light curves showing the decrease in the hard x-ray and low energy gamma-ray energy range during the hard-to-soft state transition, the several broad flares observed in these higher energies during the soft state, and then the transition back to the hard state. We also present preliminary spectra based on GBM data for the initial hard state, the spectral evolution to the soft state, and the spectral evolution back to the hard state. The implication of these results on the physical processes responsible for the hard x-ray and low energy gamma-ray emission will be discussed.

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