//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 10546 SUBJECT: GRB 100325A: Fermi GBM detection DATE: 10/03/26 14:26:50 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 06:36:08.02 UT on 25 March 2010, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 100325A (trigger 291191770/100325275). The on-ground calculated location, using the GBM trigger data, is RA = 332.3, DEC = -28.6 (J2000 degrees, equivalent to 22h 09m, -28d 36'), with an uncertainty of 1.5 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees). The angle from the Fermi LAT boresight is 9 degrees. The GBM light curve consists of a single structured pulse with a duration (T90) of 8.3 +/- 1.9 s (8-1000 keV). The time-averaged spectrum from T0-1.664 s to T0+7.552 s is best fit by a power law function with an exponential high energy cutoff. The power law index is -0.45(+0.12/-0.11) and the cutoff energy, parameterized as Epeak, is 159.3 (+12.7/-10.8) keV (CSTAT 502 for 482 d.o.f). The event fluence (8-1000 keV) in this time interval is (1.99 +/- 0.04)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+0.512 s in the 8-1000 keV band is 5.0 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// 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 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@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.