TITLE: GCN CIRCULAR NUMBER: 22424 SUBJECT: GRB 180218A: Fermi GBM Detection DATE: 18/02/19 21:26:35 GMT FROM: Suraj Poolakkil at UAH S. Poolakkil (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 15:14:05.49 UT on 18 February 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 180218A (trigger 540659650 / 180218635). This GRB was also triangulated by IPN (Svinkin et al., GCN 22423). The on-ground calculated location, using the GBM trigger data, is RA = 47.23, DEC = 46.65, with an uncertainty of 4 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 GBM light curve consists of a single bright peak with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0-1.02 s to T0+10.24 s is best fit by a Band function with Epeak= 388 +/- 13 keV, alpha = -0.62 +/- 0.03 and beta = -2.36 +/- 0.06. The event fluence (10-1000 keV) in this time interval is (5.51 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+4.28 s in the 10-1000 keV band is 65.9 +/- 0.86 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."