TITLE: GCN CIRCULAR NUMBER: 22367 SUBJECT: GRB 180120A: Fermi GBM Detection DATE: 18/01/23 22:32:28 GMT FROM: Matthew Stanbro at UAH/Fermi M. Stanbro and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 04:58:13.00 UT on 20 January 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 180120A (trigger 538117098 / 180120207) which was also detected by the CALET Gamma-ray Burst Monitor (Y. Shimizu et al. 2018, GCN 22366). The on-ground calculated location, using the GBM trigger data, is RA = 151.77, DEC = 27.79, 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 85 degrees. The GBM light curve consists of several episodes with a duration (T90) of about 29 s (50-300 keV). The time-averaged spectrum from T0+0.90 s to T0+30.59 s is best fit by a Band function with Epeak = 130 +/- 2 keV, alpha = -1.05 +/- 0.01, and beta = -2.58 +/- 0.05. The event fluence (10-1000 keV) in this time interval is (6.27 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+17.66 s in the 10-1000 keV band is 36.70 +/- 0.50 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."