TITLE: GCN CIRCULAR NUMBER: 9271 SUBJECT: GRB 090425: Fermi GBM detection DATE: 09/04/27 16:10:11 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 09:03:30.57 UT on 25 April 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090425 (trigger 262343012 / 090425377). The on-ground calculated location, using the GBM trigger data, is RA = 116.1, DEC = 69.9 (J2000 degrees, equivalent to 07h 44m, 69d 54'), with an uncertainty of 2.9 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 105 degrees. This burst was also independently detected by INTEGRAL SPI-ACS. The GBM light curve consists of three widely separated pulses and has a duration (T90) of about 72 s (8-1000 keV). The first two pulses at T0-0.6 s and T0+44 s are weak and well fit by a simple power law functions with index -1.5 +/- 0.1 and index -1.7 +/- 0.1 respectively. The third pulse observed at T0+57 s is strong and structured. The time-averaged spectrum from T0+57.537 s to T0+80.065 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -1.56 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 142 +/- 13 keV (chi squared 570 for 484 d.o.f.). A Band function fits the spectrum equally well (chi squared 566 for 483 d.o.f.) with Epeak= 69 +/- 11 keV, alpha = -1.29 +/- 0.11 and beta = -2.03 +/- 0.05. The event fluence (8-1000 keV) in this time interval is (1.3 +/- 0.2)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+57.537 s in the 8-1000 keV band is 14.0 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."