TITLE: GCN CIRCULAR NUMBER: 22689 SUBJECT: GRB 180505A: Fermi GBM detection DATE: 18/05/05 19:33:04 GMT FROM: Christian Malacaria at U of Alabama/MSFC C. Malacaria (NASA-MFSC/USRA) and E. Bissaldi (Politecnico & INFN Bari) report on behalf of the Fermi GBM Team: "At 12:57:09.91 UT on 5 May 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 180505A (trigger 547217834 / 180505540). The on-ground calculated location, using the GBM trigger data, is RA = 4.51, Dec = -59.89 (J2000 degrees), with an uncertainty of 1.2 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 angle from the Fermi LAT boresight at the GBM trigger time is 124 degrees. The GBM light curve shows multiple peaks with a duration (T90) of about 22 s (50-300 keV). The time-averaged spectrum from T0-3.5 s to T0+31 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.38 +/- 0.03 and the cutoff energy, parameterized as Epeak, is 235 +/- 19 keV The event fluence (10-1000 keV) in this time interval is (2.38 +/- 0.07)E-05 erg/cm^2. The 1-s peak photon flux measured starting from T0+20.99 s in the 10-1000 keV band is 29.2 +/- 0.8 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 233 +/- 25 keV, alpha = -1.38 +/- 0.04 and beta = -3.09 +/- 1.32. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."