TITLE: GCN CIRCULAR NUMBER: 22678 SUBJECT: GRB 180427A: Fermi GBM detection DATE: 18/04/27 18:18:10 GMT FROM: Elisabetta Bissaldi at INFN,Bari E. Bissaldi (Politecnico & INFN Bari) reports on behalf of the Fermi GBM Team: "At 10:37:03.04 UT on 27 April 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 180427A (trigger 546518228 / 180427442). The on-ground calculated location, using the GBM trigger data, is RA = 283.33, Dec = +70.30 (J2000 degrees), with an uncertainty of 1 degree (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 136 degrees. The GBM light curve shows a single FRED-like emission episode with a duration (T90) of about 26 s (50-300 keV). The time-averaged spectrum from T0 to T0+26 s is best fit by a Band function with Epeak = 108 +/- 3 keV, alpha = -0.28 +/- 0.04, and beta = -2.81 +/- 0.07. The event fluence (10-1000 keV) in this time interval is (4.92 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+5.3 s in the 10-1000 keV band is 29.2 +/- 0.8 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."