TITLE: GCN CIRCULAR NUMBER: 22626 SUBJECT: GRB 180409A: Fermi GBM observation DATE: 18/04/10 18:11:51 GMT FROM: Elisabetta Bissaldi at INFN,Bari E. Bissaldi (Politecnico & INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 08:18:18.67 UT on 9 April 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 180409A (trigger 544954703 / 180409346), which was triangulated by IPN (Hurley et al., GCN 22619) and was also detected by Konus (Frederiks et al., GCN 22621). The on-ground calculated location, using the GBM trigger data, is RA = 178.18, DEC = +36.050 (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 71 degrees. The GBM light curve consists of multiple peaks with a duration (T90) of about 13 s (50-300 keV). The time-averaged spectrum from T0-0.5 s to T0+15 s is best fit by a Band function with Epeak = 151 +/- 5 keV, alpha = -0.85 +/- 0.03, and beta = -2.33 +/- 0.05. The event fluence (10-1000 keV) in this time interval is (2.87 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10.1 s in the 10-1000 keV band is 41 +/- 1 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."