TITLE: GCN CIRCULAR NUMBER: 9832 SUBJECT: GRB 090820B: Fermi GBM detection DATE: 09/08/21 07:48:55 GMT FROM: Arne Rau at MPE Arne Rau (MPE) reports on behalf of the Fermi GBM Team: "At 12:13:16.70 UT on 20 August 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090820B (trigger 272463198 / 090820509). The on-ground calculated location, using the GBM trigger data, is RA = 318.3, DEC = -18.6 (J2000 degrees, equivalent to 21 h 13 m, -18 d 36 '), with an uncertainty of 9.6 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 32 degrees. The GBM light curve consists of two narrow peaks with a duration (T90) of about 11.2 s (8-1000 keV). The time-averaged spectrum from T0-0.128 s to T0+12.160 s is best fit by a power law function with an exponential high energy cutoff. The power law index is -1.44 +/- 0.18 and the cutoff energy, parameterized as Epeak, is 38.8 +/- 4.4 keV (chi squared 336 for 356 d.o.f.) The event fluence (8-1000 keV) in this time interval is (1.16 +/- 0.07)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0-0.128 s in the 8-1000 keV band is 6.1 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."