TITLE: GCN CIRCULAR NUMBER: 8206 SUBJECT: GRB 080904: Fermi Gamma-ray Burst Monitor detection DATE: 08/09/10 01:52:43 GMT FROM: Valerie Connaughton at MSFC Valerie Connaughton (UAH) and Alexander van der Horst (NASA/MSFC), report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 21:16:10 UT on 04 September 2008, the Fermi Gammay-Ray Burst Monitor (GBM) triggered and located a soft GRB 080904 (trigger 242255765 / 080904.886). The on-ground calculated location, using the GBM trigger data, is RA = 215.1, Dec = -32.3 (J2000 degrees) (equivalent to J2000 14h 20m, -32d 18m), with an uncertainty of 1.4 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 Large Area Telescope (LAT) boresight is 23 degrees. This GRB was about 22 s long with 1 peak, showing some substructure on the pulse rise. The time-averaged spectrum from T-4 to T+17 s is best fit by a Band function with the following parameters: alpha= 0.0 +/- 0.17 beta = -2.70 +/- 0.08 Epeak = 35 +/- 1 keV The fluence between 50 and 300 keV over these 21 seconds is 2.25 +/- 0.49 x 10^-6 erg/cm^2 with a peak flux of 3.5 +/- 0.7 photons/cm^2/sec. Between 15 and 150 keV the peak flux is 12.7 +/- 2.7 photons/cm^2/sec. According to the prescription of Sakamoto et al. 2008 (ApJ, 679, 570), the ratio of the fluences in the 25-50 keV and 50-100 keV energy ranges of 1.37 +/- 0.36 puts this in the X-Ray Flash category (XRF) but the error bar allows it to be considered, alternatively, an X-Ray Rich event (XRR). The spectral analysis results presented above are preliminary; the final results will be published in the GBM GRB Catalog."