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AGILE gamma-ray detection of a variable source in the Cygnus region

ATel #1492; F. Longo (INFN Trieste), A. Chen, S. Vercellone, P. Caraveo, A. Giuliani, S. Mereghetti, A. Pellizzoni, F. Perotti, F. Fornari, M. Fiorini (INAF/IASF Milano), A. Bulgarelli, F. Gianotti, M. Trifoglio, G. Di Cocco, C. Labanti, F. Fuschino, M. Marisaldi, M. Galli (INAF/IASF Bologna), M. Tavani, G. Pucella, F. D'Ammando, V. Vittorini, E. Costa, M. Feroci, I. Donnarumma, L. Pacciani, E. Del Monte, F. Lazzarotto, P. Soffitta, Y. Evangelista, I. Lapshov, M. Rapisarda, A. Argan, A. Trois, (INAF/IASF Roma), G. Barbiellini, E. Vallazza (INFN Trieste), P. Picozza, A. Morselli (INFN Roma-2), M. Prest (Universita` dell'Insubria), P. Lipari, D. Zanello (INFN Roma-1), P. Cattaneo (INFN Pavia), P. Giommi, C. Pittori, F. Verrecchia, P. Santolamazza, B. Preger (ASDC) and L. Salotti (ASI)
on 28 Apr 2008; 17:28 UT
Credential Certification: Andrew Chen (chen@iasf-milano.inaf.it)

Subjects: X-ray, Gamma Ray, Transient

Referred to by ATel #: 1497, 1498, 1518, 1547, 1584, 1585, 1595, 1597

The AGILE satellite, currently in a Cycle-1 pointing centered approximately in the Vulpecula region, during the observing period that started on 2008-04-10 12:00 UT, detected significant and variable gamma-ray emission from the Galactic plane from a source positionally consistent with 3EG J2020+4017. The AGILE Quicklook Analysis provides the source positional error box that is centered at Galactic coordinates l = 78.01 deg, b = 2.19 deg, and has a radius of about 1 degree.

A preliminary maximum likelihood analysis of the AGILE-GRID (Gamma-Ray Imaging Detector) data obtained between 2008-04-27 01:39 UT and 2008-04-28 01:27 UT for photon energies above 100 MeV results in a detection significance of about 5 sigma. A preliminary analysis of the Super-AGILE data over the same time period and the same sky region does not show any counterpart in the 20-60 keV energy range. The 3-sigma upper limit on the one-day average flux is 45 mCrab within the central region of the AGILE-GRID error box.

Searches for counterparts in Chandra and ROSAT coverage of the 3EG~J2020+4017 error box (Weisskopf et al. 2006, ApJ, 652, 387; Becker et al., 2004, ApJ, 615, 897) yielded no compelling counterparts. We remark that one of the many possible counterparts within the AGILE-GRID error box is the galaxy 2MASX J20183871+4041003 which has been claimed to have blazar-like characteristics (Iyudin et al., 2007, A&A, 468, 919).

We strongly encourage multi-frequency observations of the entire field of the gamma-ray source detected by AGILE in an active gamma-ray flaring state.