GCN Circular 15591
A. von Kienlin (MPE) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 13:07:56.97 UT on 09 December 2013, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 131209A (trigger 408287279 / 131209547), which was also detected by the Fermi/LAT(Vianello et al. 2013, GCN 15587), Konus-Wind (Golenetskii et al. 2013, GCN 15589) and INTEGRAL SPI-ACS. The GBM on-ground location is consistent with the error box derived by the intersection of the IPN annulus with the Fermi-LAT 1 sigma error circle (Hurley et al. 2013, GCN 15588). The GBM light curve shows a structured pulse with a duration (T90) of about 14 s (50-300 keV). The time-averaged spectrum from T0-2.560 s to T0+19.968 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.46 (+0.04/-0.04) and the cutoff energy, parameterized as Epeak, is 287 (+12/-11)keV The event fluence (10-1000 keV) in this time interval is (1.44 +/- 0.03)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+11.328 s in the 10-1000 keV band is 8.0 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 267 (+17/-14) keV, alpha = -0.41 (+0.06/-0.05) and beta = -2.79 (+0.24/-0.61). The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."