TITLE: GCN CIRCULAR NUMBER: 21776 SUBJECT: GRB 170830A: Fermi GBM observation DATE: 17/08/31 17:04:28 GMT FROM: Elisabetta Bissaldi at U.Innsbruk/IAPP M. Stanbro (UAH), E. Bissaldi (Politecnico & INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 03:14:01.95 UT on 30 August 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170830A (trigger 525755646 / 170830135). This trigger is likely associated with the transient source reported by MAXI/GSC (Yoneyama et al., GCN 21761), which was also detected by AstroSat (Bhalerao et al., GCN 21773). The on-ground calculated location, using the GBM trigger data, is RA = 275.9, DEC = -4.0, with an uncertainty of 2.6 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 100 degrees. The GBM light curve shows two peaks with a duration (T90) of about 110 s (50-300 keV). The time-averaged spectrum from T0 to T0+92 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.54 +/- 0.07 and the cutoff energy, parameterized as Epeak, is 180 +/- 40 keV. The event fluence (10-1000 keV) in this time interval is (4.20 +/- 0.11)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0 in the 10-1000 keV band is 4.6 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."