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After a gamma-ray flare, AGILE detects the Crab Nebula returning to the normal flux level

ATel #5506; F. Verrecchia, C. Pittori, F. Lucarelli (ASDC and INAF/OAR), G. Piano (INAF/IAPS), S. Vercellone (INAF/IASF-Pa), A. Bulgarelli, F. Gianotti, M. Trifoglio, V. Fioretti (INAF/IASF-Bo), M. Tavani, M. Cardillo, E. Striani (INAF/IAPS and Univ. Roma Tor Vergata), I. Donnarumma, E. Del Monte, Y. Evangelista, M. Feroci, F. Lazzarotto, L. Pacciani, P. Soffitta, E. Costa, I. Lapshov, M. Rapisarda, A. Argan, G. Pucella, S. Sabatini, V. Vittorini (INAF/IAPS), A. Chen, A. Giuliani, S. Mereghetti, P. Caraveo, F. Perotti (INAF/IASF-Mi), F. Fuschino, M. Galli, C. Labanti, M. Marisaldi, G. Di Cocco (INAF/IASF-Bo), A. Pellizzoni, A. Trois (INAF/OA-Cagliari), M. Pilia (ASTRON, the Netherlands), G. Barbiellini, F. Longo (Univ Trieste & INFN Trieste), E. Vallazza (INFN Trieste), A. Morselli, P. Picozza (INFN and Univ. Roma Tor Vergata), M. Prest (Univ. dell'Insubria), P. Lipari, D. Zanello (INFN and Univ. Roma Sapienza), P. W. Cattaneo, A. Rappoldi (INFN Pavia), S. Colafrancesco (INAF-OAR and University of the Witwatersrand, Johannesburg), A. Antonelli (INAF/OAR and ASDC), P. Giommi (ASDC), L. Salotti and G. Valentini (ASI)
on 24 Oct 2013; 17:11 UT
Credential Certification: Francesco Verrecchia (francesco.verrecchia@asdc.asi.it)

Subjects: Gamma Ray, >GeV, Neutron Star, Transient, Pulsar

Despite substantial telemetry gaps due to technical problems of the ASI Malindi ground station, AGILE confirms the enhanced gamma-ray emission (E >100 MeV) from the Crab Nebula region during the period October 17-18, 2013 (Fermi LAT ATel #5485), and reports a return to standard flux values on October 20th.

Enhanced gamma-ray emission from the source was detected by AGILE on October 18th, with a (E >100 MeV) flux F = (6.8+/-2.2) x 10^-6 ph cm^-2 s^-1 for a significance of about 5 sigma.

Since October 20th, AGILE detects a return to standard flux levels, with flux F = (2.9+/-1.3) x 10^-6 ph cm^-2 s^-1 for a 2-days integration (19-21 October, 2013).

The recent enhancement and the current flux returned at normal levels show a period of increased gamma-ray emission lasting only a few days.

This measurement was obtained with AGILE observing a large portion of the sky in spinning mode.