TITLE: GCN CIRCULAR NUMBER: 20646 SUBJECT: GRB 170208B: Fermi GBM Detection DATE: 17/02/09 15:19:35 GMT FROM: Oliver J Roberts at USRA/NASA O.J. Roberts (USRA/NASA) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 22:33:36.53 UT on the 8th of February 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170208B (trigger 508286021 / 170208940), which was also detected by Konus-Wind (Svinkin et al. 2017, GCN 20643) and Swift (Siegel et al. 2017, GCN 20632). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time using the Swift-XRT position is 54 degrees. The GBM light curve consists of a long GRB with overlapping episodes of bright emission over a duration (T90) of about 22 s (50-300 keV). The time-averaged spectrum from T0-8.0 s to T0+14.0 s is adequately fit by a Band function with Epeak = 104.1 +/- 5.5 keV, alpha = -0.83 +/- 0.05, and beta = -2.33 +/- 0.09 The event fluence (10-1000 keV) in this time interval is (1.13 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0-7.9 s in the 10-1000 keV band is 12.1 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."