TITLE: GCN CIRCULAR NUMBER: 8963 SUBJECT: GRB 090308B: Fermi GBM detection DATE: 09/03/09 21:42:26 GMT FROM: Adam Goldstein at Fermi-GBM/UAH A. Goldstein (UAH) and A.J. van der Horst (NASA/MSFC/ORAU) report on behalf of the Fermi GBM Team: "At 17:36:24.70 UT on 08 March 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090308B (trigger 258226586 / 090308734). This burst was also independently detected by INTEGRAL SPI-ACS. The on-ground calculated location, using the GBM trigger data, is RA = 22.4, DEC = -58.1 (J2000 degrees, equivalent to 01h 30m, 58d 05'), with an uncertainty of 2.3 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 50 degrees. The GBM light curve consists of two peaks with substructure with a duration (T90) of about 2.11 s (8-1000 keV). The time-averaged spectrum from T0-0.25 s to T0+1.53 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -0.54 +/- 0.11 and the cutoff energy, parameterized as Epeak, is 710.3 +/- 100.0 keV (chi squared 342 for 362 d.o.f.). The event fluence (8-1000 keV) in this time interval is (3.46 +/- 0.13)E-06 erg/cm^2. The 0.128-sec peak photon flux measured starting from T0+0.64 s in the 8-1000 keV band is 14.22 +/- 0.91 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."