TITLE: GCN CIRCULAR NUMBER: 20652 SUBJECT: GRB 170209A: Fermi GBM Detection DATE: 17/02/09 22:26:43 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 01:08:38.08 UT on the 9th of February 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170209A (trigger 508295323 / 170209048), for which MASTER reported an OT in follow-up observations of the reported GBM location region (Podesta et al. 2017, GCN 20650). The on-ground calculated location using the GBM trigger data is, RA = 113.40, DEC = -49.64 (J2000 degrees), equivalent to J2000 7h 33m, -49d 38', with an uncertainty of 3.22 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg. error and a small tail suffering a larger than 10 deg. systematic error [Connaughton et al. 2015, ApJS, 216, 32]). The angle from the Fermi LAT boresight at the GBM trigger time is 120 degrees. The GBM light curve consists of a long GRB with two bright episodes of emission over a duration (T90) of about 40 s (50-300 keV). The time-averaged spectrum from T0+0 s to T0+40.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.95 +/- 0.07 and the cutoff energy, parameterized as Epeak is 132 +/- 9 keV. The event fluence (10-1000 keV) in this time interval is (9.34 +/- 0.37)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.9 s in the 10-1000 keV band is 12.6 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."