TITLE: GCN CIRCULAR NUMBER: 22289 SUBJECT: GRB 171227A: Fermi GBM detection DATE: 17/12/27 18:55:27 GMT FROM: C. Michelle Hui at MSFC/Fermi-GBM C. M. Hui (NASA/MSFC) reports on behalf of the Fermi GBM Team: At 00:00:13.40 UT on 27 December 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 171227A (trigger 536025618/171227000), also detected by AGILE/MCAL (Verrecchia et al. GCN 22288). The on-ground calculated location, using the GBM trigger data, is RA = 280.7 , DEC = -35.0 (J2000 degrees, equivalent to 18h 42m, -35d 0.0'), 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 with a systematic error of more than 10 deg [Connaughton et al. 2015, ApJS, 216, 32] ). The angle from the Fermi LAT boresight is 120 degrees. The GBM light curve shows several peaks with decreasing amplitudes and a duration (T90) of about 38 s (50-300 keV). The time-averaged spectrum from T0+0.0 s to T0+58.2 s is adequately fit by a Band function with Epeak = 771 +/- 14 keV, alpha = -0.87 +/- 0.01, and beta = -2.47 +/- 0.04. The event fluence (10-1000 keV) in this time interval is (305.3 +/- 1.3) E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+19.4 s in the 10-1000 keV band is 90.3 +/- 0.7 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog.