TITLE: GCN CIRCULAR NUMBER: 18081 SUBJECT: GRB 150727A: Fermi GBM detection DATE: 15/07/28 06:25:51 GMT FROM: George A. Younes at George Washington U G. Younes (GWU) reports on behalf of the Fermi GBM Team: "At 19:01:56.35 UT on July 27 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150727A (trigger 459716520/150727793), which was also detected by Swift (Cenko et al. 2015, GCN 18076). The GBM on-ground location, using the Fermi GBM trigger data, is consistent with the Swift/XRT location. The angle of the burst direction to the Fermi LAT boresight is 46 degrees. The GBM light curve shows a FRED-like (fast-rise exponential-decay) pulse with a duration (T90) of about 50s (50-300 keV). The time-averaged spectrum from T0-4s to T0+56s is well fit by a power law with an exponential high-energy cutoff. The power law index is -0.7 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 149 +/- 10 keV. The event fluence (10-1000 keV) in this time interval is (7.9 +/- 0.3)E-06 ergs/cm^2. The 1.0-sec peak photon flux measured starting from T0+5.0s in the 10-1000 keV band is 2.1 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."