TITLE: GCN CIRCULAR NUMBER: 8960 SUBJECT: GRB 090306C: Fermi GBM detection DATE: 09/03/09 14:59:13 GMT FROM: Arne Rau at MPE Arne Rau (MPE) reports on behalf of the Fermi GBM Team: "At 05:52:05.35 UT on 06 March 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090306C (trigger 258011527 / 090306245). The on-ground calculated location, using the GBM trigger data, is RA = 135.0, DEC = +51.7 (J2000 degrees, equivalent to 09 h 00 m, 51 d 36 '), with an uncertainty of 5.5 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 14 degrees. The GBM light curve shows one main peak lasting about 5s followed by a broader tail with a total duration (T90) of about 38.8 s (8-1000 keV). The time-averaged spectrum from T0-4.096 s to T0+6.144 s is adequately fit by a power law function with an exponential high energy cutoff at 107 +/- 16 keV and with index -0.58 +/- 0.29 (chi squared 380 for 381 d.o.f.). The event fluence (8-1000 keV) in this time interval is (9.0 +/- 2.2)E-07 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.024 s in the 8-1000 keV band is 2.4 +/- 0.1 ph/s/cm^2. A Band function fits the spectrum equally well (chi squared 378 for 380 d.o.f.) with Epeak= 87 +/- 25 keV, alpha = -0.32 +/- 0.54 and beta = -2.28 +/-0.43. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."