GCN Circular 9524
Subject
GRB 090618: AGILE observations
Date
2009-06-18T15:21:44Z (16 years ago)
From
Marco Feroci at IASF/INAF <feroci@iasf-roma.inaf.it>
F. Longo, E. Moretti, G. Barbiellini, E. Vallazza (INFN Trieste),
M.Trifoglio, A. Bulgarelli, F. Gianotti F. Fuschino, M. Marisaldi,
C.Labanti, M.Galli, G.DiCocco (INAF/IASF Bologna), S. Cutini, C.
Pittori (ASDC), M.Tavani, E.Striani, G. Pucella, F. D'Ammando,
V.Vittorini, A. Argan, A. Trois, G. Piano, S. Sabatini
(INAF/IASF Rome), E. Del Monte, M. Feroci, Y. Evangelista, I. Donnarumma,
L. Pacciani, P. Soffitta, E. Costa, F.Lazzarotto, I. Lapshov, M. Rapisarda
(INAF/IASF Rome) A. Giuliani, A. Chen, S. Mereghetti, F. Perotti, P.
Caraveo (INAF/IASF Milano), A. Pellizzoni, M. Pilia (INAF/OA Cagliari), S.
Vercellone (INAF/IASF Palermo), P. Picozza, A. Morselli (INFN Roma-2), M.
Prest (Universita` dell'Insubria), P. Lipari, D. Zanello (INFN Roma-1), A.
Rappoldi, P. Cattaneo (INFN Pavia) and P. Giommi, P. Santolamazza, F.
Verrecchia (ASDC) and L. Salotti (ASI), on behalf of the AGILE Team,
report:
The AGILE satellite detected GRB 090618 (P. Schady et al. GCN #9512)
at about 36 degrees off axis.
Super-AGILE, operating in the 18-60 keV energy range, triggered and
localized the burst in the 1-D region of the field of view at a position
consistent with the Swift/BAT localization. The emission from this bright
GRB with a complex lightcurve was detected at high significance despite
the large off-axis direction.
AGILE-MCAL, operating in the 350 keV - 100 MeV energy range, triggered
this GRB at 08:28:24.772 UT (T0). The MCAL overall burst duration is
about 100 sec. The burst is composed by three main pulses, the
brightest starting at T0+62sec and lasting about 14 seconds.
The total MCAL spectrum between T0 and T0+120 sec can be fit by a
simple powerlaw with photon index 3.16 (-0.30, +0.39) (90% c.l.),
with reduced chi^2 0.99 (9 d.o.f.), in the 0.5-10 MeV energy range.
The estimated fluence is (3.2 +/- 0.6) 10^{-5} erg cm^-2 in the same
energy range.
From a preliminary analysis of the AGILE-GRID data in the energy range
30 MeV-30 GeV no significant gamma-ray emission above 30 MeV is detected
in the GRB error box during both the first and second main pulse for
a total duration of about 130 sec. A preliminary upper limit is 0.1
ph cm^-2 over a 130 s duration.
GRB 090618 provides a clear evidence for a class of GRBs bright below
a few MeV, showing the lack of significant gamma-ray emission above 30
MeV.