TITLE: GCN CIRCULAR NUMBER: 13644 SUBJECT: GRB 120811B: Fermi GBM observation DATE: 12/08/15 02:22:29 GMT FROM: Shaolin Xiong at UAH Shaolin Xiong (UAH) and Chip Meegan (USRA) report on behalf of the Fermi GBM Team: "At 00:20:31.288 UT on 11 August 2012, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 120811B (trigger 366337233 / 120811014), which was also located by the IPN (S. Golenetskii et al. 2012, GCN 13627). The GBM on-ground location is consistent with the IPN position. The angle from the Fermi LAT boresight is 85 degrees. The GBM light curve consists of two pulses with a duration (T90) of about 0.448 s (50-300 keV). The time-averaged spectrum from T0-0.064 s to T0+0.384 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.29 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 1294 +/- 145 keV. The event fluence (10-1000 keV) in this time interval is (2.45 +/- 0.10)E-6 erg/cm^2. The 64 ms peak photon flux measured starting from T0+0.064 s in the 10-1000 keV band is 21.0 +/- 1.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."