EPISODIC TRANSIENT GAMMA-RAY EMISSION FROM THE MICROQUASAR CYGNUS X-1

Journal Article · Sat Mar 20 00:00:00 EDT 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/712/1/L10; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21305096

Sabatini, S; Tavani, M; Vittorini, V; Piano, G; Del Monte, E; Feroci, M; Argan, A; D'Ammando, F; Costa, E; De Paris, G ^[1]; Striani, E ^[2]; Bulgarelli, A; Trifoglio, M; Gianotti, F; Di Cocco, G ^[3]; De Pasquale, F ^[4]; Barbiellini, G ^[5]; Caraveo, P; Chen, A W ^[6]; Cattaneo, P W ^[7]

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1. INAF/IASF-Roma, I-00133 Roma (Italy)
2. Dip. di Fisica, Univ. Tor Vergata, I-00133 Roma (Italy)
3. INAF/IASF-Bologna, I-40129 Bologna (Italy)
4. ITAB, Via dei Vestini 33, I-66100 Chieti (Italy)
5. Dip. Fisica and INFN Trieste, I-34127 Trieste (Italy)
6. INAF/IASF-Milano, I-20133 Milano (Italy)
7. INFN-Pavia, I-27100 Pavia (Italy)

Cygnus X-1 (Cyg X-1) is the archetypal black hole binary system in our Galaxy. We report the main results of an extensive search for transient gamma-ray emission from Cygnus X-1 carried out in the energy range 100 MeV-3 GeV by the AGILE satellite, during the period 2007 July-2009 October. The total exposure time is about 300 days, during which the source was in the 'hard' X-ray spectral state. We divided the observing intervals in 2-4 week periods, and searched for transient and persistent emission. We report an episode of significant transient gamma-ray emission detected on 2009 October 16 in a position compatible with Cyg X-1 optical position. This episode, which occurred during a hard spectral state of Cyg X-1, shows that a 1-2 day time variable emission above 100 MeV can be produced during hard spectral states, having important theoretical implications for current Comptonization models for Cyg X-1 and other microquasars. Except for this one short timescale episode, no significant gamma-ray emission was detected by AGILE. By integrating all available data, we obtain a 2{sigma} upper limit for the total integrated flux of F {sub {gamma}}{sub ,U.L.} = 3 x 10{sup -8} ph cm{sup -2} s{sup -1} in the energy range 100 MeV-3 GeV. We then clearly establish the existence of a spectral cutoff in the energy range 1-100 MeV that applies to the typical hard state outside the flaring period and that confirms the historically known spectral cutoff above 1 MeV.

• OSTI ID: 21305096
• Journal Information: Astrophysical Journal Letters, Vol. 712, Issue 1; Other Information: DOI: 10.1088/2041-8205/712/1/L10; Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
BLACK HOLES
FLARING
GALAXIES
GAMMA RADIATION
GEV RANGE 01-10
MEV RANGE 100-1000
PHOTON EMISSION
SATELLITES
STARS
X RADIATION