Speaker
Dr
Sabina Sabatini
(INAF IAPS)
Description
Gamma-ray observations by the AGILE satellite during the period mid-2007-2010 of the black hole binary system Cygnus X-1 will be presented. The source was observed both in the most common hard state and during a remarkably prolonged `soft state' phase (June 2010 -- May
2011). Previous 1--10 MeV observations of Cyg X-1 in this state hinted at a possible existence of a non-thermal particle component with substantial modifications of the Comptonized emission from the inner accretion disk. Our AGILE data provide a significant upper limit for the gamma-ray emission above 100 MeV, excluding the existence of prominent non-thermal emission above 100 MeV during the soft state of Cygnus X-1. We will discuss theoretical implications of our findings in the context of high-energy emission models of black hole accretion. We also discuss possible gamma-ray flares detected by AGILE. In particular, we report a weak but important candidate for enhanced emission which occurred at the end of June 2010 (2010-06-30 10:00 - 2010-07-02 10:00 UT) exactly in coincidence with a hard-to-soft state transition and before an anomalous radio flare.
Primary author
Dr
Sabina Sabatini
(INAF IAPS)
