GRB 170522A: Fermi GBM detection

"At 15:45:35.28 UT on 22 May 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170522A (trigger 517160740 / 170522657). The on-ground calculated location, using the GBM trigger data, is RA = 135.45, DEC = 27.12, with an uncertainty of 1.0 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 initial angle from the Fermi LAT boresight to the GBM ground location is 50 degrees. The GBM light curve consists of 1 peak with a duration (T90) of about 7 s (50-300 keV). The time-averaged spectrum from T0-0.00 s to T0+8.32 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.41 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 344 +/- 8 keV. The event fluence (10-1000 keV) in this time interval is (2.31 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.58 s in the 10-1000 keV band is 23.35 +/- 0.37 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 314 +/- 11 keV, alpha = -0.36 +/- 0.03 and beta = -2.63 +/- 0.15. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."