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AGILE monitoring of the strongly variable gamma-ray emission from the Crab Nebula

ATel #3286; E. Striani (Univ. Tor Vergata), G. Piano (INAF/IASF Roma), M. Tavani (INAF/IASF Roma and Univ. Tor Vergata), A. Bulgarelli (INAF/IASF Bologna), C. Pittori, F. Verrecchia (ASDC), V. Vittorini (INAF/IASF Roma), F. Gianotti, M. Trifoglio (INAF/IASF Bologna), A. Argan, A. Trois, G. De Paris, S. Sabatini, E. Costa, I. Donnarumma, M. Feroci, L. Pacciani, E. Del Monte, F. Lazzarotto, P. Soffitta, Y. Evangelista, I. Lapshov (INAF-IASF-Rm), P. Caraveo, A. Chen, A. Giuliani, S. Mereghetti, F. Perotti (INAF-IASF-Milano), M. Marisaldi, G. Di Cocco, C. Labanti, F. Fuschino, M. Galli (INAF/IASF Bologna), G. Pucella, M. Rapisarda (ENEA-Roma), S. Vercellone, F. D'Ammando (IASF-Pa), A. Pellizzoni, M. Pilia (INAF/OA-Cagliari), G. Barbiellini, F. Longo (INFN Trieste), P. Picozza, A. Morselli (INFN and Univ. Tor Vergata), M. Prest (Universita` dell'Insubria), P. Lipari, D. Zanello (INFN Roma-1), P. W. Cattaneo, A. Rappoldi (INFN Pavia), P. Giommi, P. Santolamazza, F. Lucarelli, (ASDC), G. Valentini, L. Salotti (ASI)
on 16 Apr 2011; 16:10 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Marco Tavani (tavani@iasf-roma.inaf.it)

Subjects: Gamma Ray, Neutron Star, Supernova Remnant, Transient, Pulsar

Referred to by ATel #: 4239, 4855

Strongly variable gamma-ray emission above 100 MeV continues to be detected by AGILE from a source positionally consistent with the Crab Nebula.

After a telemetry gap that AGILE experienced on April 14, 2011 (in partial coincidence with the strong gamma-ray flare reported by Fermi-LAT in ATel # 3284) the AGILE-GRID detected the following gamma-ray flux above 100 MeV (pulsar plus nebula):

MJD=55666.44-55667.44, 2011-04-15 10:40 UT - 2011-04-16 10:38 UT, F = (19.6 +/- 3.7) 10^{-6} ph/cm^2/sec.

(We recall that the long timescale average flux from the Crab pulsar + Nebula in the AGILE-GRID energy range above 100 MeV is F = (2.2 +/- 0.15) 10^{-6} ph/cm^2/sec).

This extreme gamma-ray emission from the Crab Nebula follows the activity recently reported by Fermi-LAT and AGILE in ATels # 3276, # 3282, # 3284). Follow-up X-ray observations were carried out by Swift (ATel # 3279) as well as Chandra (ATel # 3283).

The Crab Nebula is currently the brightest gamma-ray source in the sky with a flux approximately twice that of the Vela pulsar. Short-timescale variations of the AGILE gamma-ray signal show variability on a 12 hr timescale or less.

Multifrequency observations of the Crab Nebula are crucial to monitor this remarkable state of emission, and we strongly encourage these observations despite the current unfavorable sky position of the Crab.