TITLE: GCN CIRCULAR NUMBER: 8280 SUBJECT: GRB 080913B: Fermi GBM detection DATE: 08/09/21 15:32:20 GMT FROM: Bill Paciesas at UAH Bill Paciesas (UAH), Alexander van der Horst (NASA/MSFC) and Adam Goldstein (UAH), report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 17:38:31 UT on 13 September 2008, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 080913B (trigger 243020312 / 080913.735). The on-ground calculated location, using the GBM trigger data, is RA = 46.3, Dec = -4.6 (J2000 degrees) (equivalent to J2000 3h 05m, -4d 36'), with an uncertainty of 3.3 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 Large Area Telescope (LAT) boresight is 71 degrees. This GRB was about 140 s long consisting of several peaks with a main emission period of 30 seconds. The time-averaged spectrum from T-2 to T+28 s is best fit by a power law with exponential cut-off, with a power-law index of -0.69 +/- 0.16 and a cut-off energy, parameterized as Epeak, of 114 +/- 14 keV. The fluence between 50 and 300 keV over these 30 seconds is (2.2 +/- 0.5) x 10^-6 erg/cm^2. The spectral analysis results presented above are preliminary; the final results will be published in the GBM GRB Catalog."