TITLE: GCN CIRCULAR NUMBER: 8918 SUBJECT: GRB 090228: Fermi GBM detection DATE: 09/02/28 17:42:15 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 04:53:20.91 UT on 28 February 2009, the Fermi Gamma-Ray Burst Monitor triggered and located the bright short GRB 090228 (trigger 257489602 / 090228204). The on-ground calculated location, using the GBM trigger data, is RA = 106.8, DEC = -24.3 (J2000 degrees, equivalent to 07h 07m, -24d 18'), with a statistical uncertainty of less than 1 degree (radius, 1-sigma containment) and an additional systematic error which is currently estimated to be 2 to 3 degrees. The angle from the Fermi LAT boresight is 16 degrees This short GRB shows a single bright pulse followed by a peak of significantly lesser intensity. The burst duration (T90) is about 0.8 s (8-1000 keV). The time-averaged spectrum from T0-0.016 s to T0+0.176 s is best fit by a Band function with Epeak = 849 +/- 44 keV, alpha = -0.35 +/- 0.04, and beta = -2.98 +/- 0.25 (chi squared 732.29 for 723 d.o.f.). The event fluence (8-1000 keV) in this time interval is (6.1 +/- 0.09)E-06 erg/cm^2. The 0.32-sec peak photon flux measured starting from T0 s in the 8-1000 keV band is 133 +/- 8 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."