[vsnet-grb-info 12055] GRB 120711A: Fermi LAT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13444
SUBJECT: GRB 120711A: Fermi LAT detection
DATE:    12/07/11 17:29:37 GMT
FROM:    Thomas P.H. Tam at Nat.Tsing Hua U.  <grbtom at gmail.com>

P.H.T. Tam, K.L. Li and A.K.H. Kong (NTHU) report:

We report on the Fermi Large Area Telescope (LAT) detection of >100 MeV
gamma-ray emission from the direction of the bright GRB 120711A, which
triggered INTEGRAL (Gotz et al., GCN 13434), MAXI/GSC (Serino et al., GCN
13436), and Fermi/GBM (Gruber et al., GCN 13437). The GRB position was
outside the LAT field of view at the GRB onset (c.f. GCN 13437). However,
gamma-ray emission up to around 2 GeV was detected from the GRB direction
from 0.8 ks to ~7 ks after the burst. Such duration is one of the longest
ever observed for a GRB in GeV domain.

Using the data obtained from the above period, an unbinned likelihood
analysis resulted in a detection significance of ~7 sigma, and a photon
spectral index of -1.8+-0.3. We localized the LAT emission to be at RA, DEC
(J2000 deg) = 94.58, -70.93, with a statistical error of ~0.17 deg (68%
CL), which is compatible with the Swift/XRT position (Beardmore et al., GCN
13442).