GAMMA-RAY OBSERVATIONS OF CYGNUS X-1 ABOVE 100 MeV IN THE HARD AND SOFT STATES

Journal Article · Mon Apr 01 00:00:00 EDT 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/766/2/83· OSTI ID:22167521

Sabatini, S.; Tavani, M.; Del Santo, M.; Campana, R.; Evangelista, Y.; Piano, G.; Del Monte, E.; Giusti, M.; Striani, E. ^[1]; Coppi, P. ^[2]; Pooley, G. ^[3]; Chen, A.; Giuliani, A. ^[4]; Bulgarelli, A. ^[5]; Cattaneo, P. W. ^[6]; Colafrancesco, S. ^[7]; Longo, F. ^[8]; Morselli, A. ^[9]; Pellizzoni, A. ^[10]; Pilia, M. ^[11] ; others, and

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1. INAF/IAPS-Roma, I-00133 Roma (Italy)
2. Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States)
3. Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE (United Kingdom)
4. INAF/IASF-Milano, I-20133 Milano (Italy)
5. INAF/IASF-Bologna, I-40129 Bologna (Italy)
6. INFN-Pavia, I-27100 Pavia (Italy)
7. INAF-OAR, I-00040 Monteporzio Catone (Italy)
8. Dip. Fisica and INFN Trieste, I-34127 Trieste (Italy)
9. INFN Roma Tor Vergata, I-00133 Roma (Italy)
10. INAF-OAC, I-09012 Capoterra (Italy)
11. ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo (Netherlands)

We present the results of multi-year gamma-ray observations by the AGILE satellite of the black hole binary system Cygnus X-1. In a previous investigation we focused on gamma-ray observations of Cygnus X-1 in the hard state during the period mid-2007/2009. Here we present the results of the gamma-ray monitoring of Cygnus X-1 during the period 2010/mid-2012 which includes a remarkably prolonged 'soft state' phase (2010 June-2011 May). 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, averaged over the mid-2010/mid-2011 soft state of Cygnus X-1, provide a significant upper limit for gamma-ray emission above 100 MeV of F{sub soft} < 20 Multiplication-Sign 10{sup -8} photons cm{sup -2} s{sup -1} , excluding the existence of prominent non-thermal emission above 100 MeV during the soft state of Cygnus X-1. We 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 addition to a previously reported episode observed by AGILE in 2009 October during the hard state, we report a weak but important candidate for enhanced emission which occurred at the end of 2010 June (2010 June 30 10:00-2010 July 2 10:00 UT) exactly coinciding with a hard-to-soft state transition and before an anomalous radio flare. An appendix summarizes all previous high-energy observations and possible detections of Cygnus X-1 above 1 MeV.

• OSTI ID: 22167521
• Journal Information: Astrophysical Journal, Vol. 766, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
BINARY STARS
BLACK HOLES
COMPTON EFFECT
GAMMA DETECTION
GAMMA RADIATION
MEV RANGE
PHOTONS
SATELLITES