[vsnet-grb-info 9060] GRB 100325A: Fermi LAT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10548
SUBJECT: GRB 100325A: Fermi LAT detection
DATE:    10/03/27 22:09:54 GMT
FROM:    Francesco de Palma at U of INFN Bari  <francesco.depalma at ba.infn.it>

Francesco de Palma (INFN and Università di Bari),Takeshi Uehara 
(Hiroshima University), Johan Bregeon (INFN Pisa), Veronique Pelassa
(CNRS/IN2P3/LPTA), Jim Chiang (SLAC), Fred Piron (LPTA), Nicola Omodei
(Stanford) report on behalf of the Fermi LAT collaboration:

At 06:36:08.02 UT on 25 March 2010, the Fermi Large Area Telescope (LAT)
detected gamma rays from the GRB 100325A, which was triggered and 
located by the Fermi Gamma-ray Burst Monitor (GBM)
(trigger 291191770/100325.275,GCN10546). The angle of the GBM position
position with respect to the LAT boresight was ~9.2 degrees at the time
of the LAT detection, close to the center of the LAT field of view.

The data from the Fermi LAT shows a weak increase in the event rate
that is spatially and temporally correlated with the GBM emission.
It is a relatively weak detection (~>4 sigma) with 4 photons above
100 MeV within 9 seconds after the GBM trigger.
The highest energy photon has an energy just above 800 MeV.

The best LAT on-ground localization is found to be (RA, Dec = 330.24,
-26.47) (J2000) with a 90% containment radius of 0.9 deg 
(statistical; 68% containment radius: 0.6 deg) which is consistent with 
the GBM localization. The observed flux (100 MeV-300 GeV) from this 
location is 1.18 +/- 0.76 e-04 (ph/cm^2/s).

Further analysis is ongoing.

The point of contact for this burst is Francesco de Palma
(francesco.depalma at ba.infn.it)

The Fermi LAT is a pair conversion telescope designed to cover the
energy band from 20 MeV to greater than 300 GeV. It is the product of
an international collaboration between NASA and DOE in the U.S. and 
many scientific institutions across France, Italy, Japan and Sweden.