TITLE: GCN CIRCULAR NUMBER: 22170 SUBJECT: GRB 171126A: Fermi GBM detection DATE: 17/11/26 18:18:29 GMT FROM: C. Michelle Hui at MSFC/Fermi-GBM C. M. Hui (NASA/MSFC) and C. Meegan (UAH) reports on behalf of the Fermi GBM Team: At 05:38:43.71 UT on 26 November 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 171126A (trigger 533367528/171126235). The on-ground calculated location, using the GBM trigger data, is RA = 237.84, DEC = +46.76 (J2000 degrees, equivalent to 15h 51m, +46d 42'), with an uncertainty of 3.29 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 trigger resulted in an Autonomous Repoint Request (ARR) by the GBM Flight Software owing to the high peak flux of the GRB. This ARR was accepted and the spacecraft slewed to the GBM in-flight location. The angle from the Fermi LAT boresight is 50 degrees. The GBM light curve shows a single bright peak followed by a secondary emission with a duration (T90) of about 1.47s (50-300 keV). The time-averaged spectrum from T0+0.0s to T0+2.08s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -0.66 +/- 0.05 and the cutoff energy, parameterized as Epeak, is 89.36 +/- 2.52 keV. The event fluence (10-1000 keV) in this time interval is (2.074 +/- 0.042)E-06 erg/cm^2. The 64ms peak photon flux measured starting from T0+0.192s in the 10-1000 keV band is 97.21 +/- 6.07 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog.