[vsnet-grb-info 11774] GRB 120328B: Fermi-LAT Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13165
SUBJECT: GRB 120328B: Fermi-LAT Observations
DATE:    12/03/28 23:43:31 GMT
FROM:    Giacomo Vianello at SLAC  <giacomov at slac.stanford.edu>

G.Vianello (CIFS/SLAC), V. Vasileiou (CNRS/IN2P3/LUPM), D.Kocevski
(Stanford) report on behalf of the Fermi LAT Team:

Fermi-LAT has detected high energy emission from GRB 120328B in ground
analysis. The GRB was triggered on by Fermi-GBM at 06:26:20 on March
28, 2012 (trigger 354608782, GCN 13163), and by Konus-Wind (GCN
13158).

The best available position, provided by the IPN (GCN 13157), is ~66
deg off-axis, outside of the Fermi/LAT nominal field of view for the
standard data analysis. Moreover, the zenith angle is ~105 deg, well
within the region strongly contaminated by gamma-ray emission from the
Earth's limb.

Using a non-standard data selection most sensitive in the tens-of-MeV
energy range and with a broader acceptance, we
significantly detected the burst during the time interval of the
prompt emission between T0 and ~T0+30 s. The significance of the
excess corresponds to ~8 sigma. This data selection has insufficient
spatial resolution to provide a reliable LAT localization.

The GRB position entered the nominal field of view of the LAT ~2200 s
after the trigger. A standard likelihood analysis on the time interval
T0+2200 s - T0+3500 s does not show any excess at the position of the
GRB.

The Fermi LAT point of contact for this burst is Giacomo Vianello
(giacomov at slac.stanford.edu).