TITLE: GCN CIRCULAR NUMBER: 9866 SUBJECT: GRB 090902B: Fermi GBM detection of a bright burst DATE: 09/09/02 21:19:03 GMT FROM: Elisabetta Bissaldi at MPE Elisabetta Bissaldi (MPE) and Valerie Connaughton (UAH) report on behalf of the Fermi GBM Team: "At 11:05:08.31 UT on 2 September 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090202B (trigger 273582310 / 090902462). The on-ground calculated location, using the GBM trigger data, is RA = 264.5, DEC = 26.5 (J2000 degrees, equivalent to 17h 38m, 26d 30'), with an uncertainty of 1.0 degree (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 52 degrees. Moreover, this burst was bright enough to result in a Fermi spacecraft repointing maneuver. The burst was also independently detected by INTEGRAL SPI-ACS. The GBM light curve consists of a bright pulse with a duration of about 21 s. The time-averaged spectrum between 50 keV and 40 MeV from T0 to T0+22 s is well fit by a Band function with Epeak = 775 +/- 11 keV, alpha = -0.696 +/- 0.012 and beta = -3.85 (+0.21/-0.31). The event fluence (50 keV - 10 MeV) in this time interval is (3.74 +/- 0.03)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+14 s in the 50 keV - 10 MeV band is 46.1 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."