TITLE: GCN CIRCULAR NUMBER: 21715 SUBJECT: GRB 170826A: Fermi GBM detection DATE: 17/08/26 19:00:17 GMT FROM: Suraj Poolakkil at UAH S. Poolakkil (UAH), E. Bissaldi (Politecnico & INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 08:51:07.51 UT on 26 August 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170826A (trigger 525430272/ 170826369). The on-ground calculated location, using the GBM trigger data, is RA = 82.4, DEC = 32.8, with an uncertainty of 7.2 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 101 degrees. The GBM triggered on a single pulse over a total duration (T90) of about 0.2 s (50-300 keV). The time-averaged spectrum from T0-0.2 to T0+0.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.05 +/- 0.11 and the cutoff energy, parameterized as Epeak, is 685 +/- 236 keV. The event fluence (10-1000 keV) in this time interval is (8.2 +/- 0.6)E-07 erg/cm^2. The 64 ms peak photon flux measured starting from T0+0.1 s in the 10-1000 keV band is 18.6 +/- 2.1 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." -- Suraj Poolakkil Fermi GBM Graduate Research Assistant Dept. of Space Science University of Alabama in Huntsville