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AGILE gamma-ray detection of Cygnus X-1

ATEL # 2715; S. Sabatini (INAF/IASF-Rm), E. Striani (Univ. Roma Tor Vergata and INFN Roma), F. Verrecchia(ASDC), M. Tavani (INAF/IASF-Rm, and Univ. Tor Vergata), Y. Evangelista, E. Del Monte (INAF/IASF-Rm), C. Pittori (ASDC), A. Bulgarelli, F. Gianotti, M. Trifoglio (INAF/IASF-Bo), I. Donnarumma, M. Feroci, F. Lazzarotto, L. Pacciani, P. Soffitta, E. Costa, I. Lapshov, M. Rapisarda, A. Argan, G. Piano, G. Pucella, A. Trois, V. Vittorini (INAF/IASF-Rm), A. Chen, A. Giuliani, S. Mereghetti, P. Caraveo, F. Perotti (INAF/IASF-Mi), A. Pellizzoni, M. Pilia (INAF/OA-Cagliari), G. Barbiellini, F. Longo, E. Moretti, E. Vallazza (INFN Trieste), F. Fuschino, M. Galli, C. Labanti, M. Marisaldi, G. Di Cocco (INAF/IASF-Bo), A. Morselli, P. Picozza (INFN and Univ. Roma Tor Vergata), M. Prest (Universita` dell'Insubria), P. Lipari, D. Zanello (INFN and Univ. Roma Sapienza), P.W. Cattaneo, A. Rappoldi (INFN Pavia), S. Vercellone, F. D'Ammando (INAF/IASF-Pa), F. Lucarelli, P. Santolamazza, S. Colafrancesco, P. Giommi (ASDC), L. Salotti (ASI)
on 2 Jul 2010; 13:37 UT
Password Certification: Sabina Sabatini (sabina.sabatini@iasf-roma.inaf.it)

Subjects: Gamma Ray, Binaries, Black Holes, Transients
Referred to by ATEL #: 2734, 2751

Following the MAXI/GSC detection of a new soft X-ray brightening in Cygnus X-1 (ATel #2711) and the subsequent X-ray increased emission reported by RXTE-ASM (ATel #2714), indicating a possible transition of the source to the soft spectral state, we carried out follow up analysis for gamma-ray emission in AGILE data.

Integrating from 2010-06-30 10:00 UT to 2010-07-02 10:00 UT, a maximum likelihood analysis yields a flux excess above 100 x 10-8 ph/cm2/s (E > 100 MeV) in a position consistent with the black hole binary Cygnus X-1. We note that AGILE has monitored the Cygnus region since July 2007 and the 2-sigma upper limit for the gamma-ray flux above 100 MeV is 3x10-8 ph/cm2/s at the position of Cygnus X-1.

Gamma-ray flaring activity for a source positionally consistent with Cygnus X-1 was previously reported by AGILE in ATel #2512 with a flux above 250x10-8 ph/cm2/s.

These measurements were obtained with AGILE observing a large portion of the sky in a spinning mode.


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R. E. Rutledge , Editor
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