TITLE: GCN CIRCULAR NUMBER: 20728 SUBJECT: GRB 170222A: Fermi GBM observation DATE: 17/02/22 22:52:42 GMT FROM: Rachel Hamburg at UAH R. Hamburg (UAH), E. Bissaldi (Politecnico & INFN Bari), and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 05:00:59.08 UT on 22 February 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170222A (trigger 509432464 / 170222209), which was also reported by IPN (Hurley et al. 2017, GCN 20722). The on-ground calculated location, using the GBM trigger data, is RA = 312.10, DEC = +12.45 (J2000 degrees, equivalent to 20h 48m, 12d 27'), with an uncertainty of 3.6 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] ). Although the GBM localization is not consistent within 3 sigma of the IPN localization, the GBM localization places this event in the same part of the sky and is the same event as that reported by IPN. The angle from the Fermi LAT boresight at the GBM trigger time using the IPN position is 120 degrees. The GBM light curve shows a single multi-peaked emission episode with a duration (T90) of about 1.7 s (50-300 keV). The time-averaged spectrum from T0-0.64 s to T0+2.43 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.70 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 862 +/- 118 keV. The event fluence (10-1000 keV) in this time interval is (5.31 +/- 0.19)E-06 erg/cm^2. The 0.64-sec peak photon flux measured starting from T0+1.15 s in the 10-1000 keV band is 17.4 +/- 1.9 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."