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
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.