GCN Circular 15331
P. Jenke (UAH) reports on behalf of the Fermi GBM Team: At 17:47:34.99 UT on October 11 2013, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 131011A (trigger 403206457/131011741). A candidate optical afterglow was found by iPTF (Kasliwal et al. 2013, GCN 15324) using the GBM on-ground location. Additional follow-ups confirmed that the optical source has faded (Xu et al. 2013, GCN 15325) and has a redshift of z = 1.874 (Rau et al. 2013, GCN 15330). A weak X-ray source consistent with the optical afterglow was detected by the Swift XRT (Page et al. 2013, GCN 15329). The angle of the burst direction to the Fermi LAT boresight is 74 degrees. The GBM light curve consists of one main peak and a small post burst with a combined duration (T90) of about 77 s (50-300 keV). The time-averaged spectrum from T0-3 s to T0+25s is well fit by a Band function with Epeak of 220 +/- 30 keV. Alpha = -0.79 +/- 0.08 and Beta = -2.0 +/- 0.1. The event fluence (10-1000 keV) in this time interval is (6.60 +/- 0.03)E-05 erg/cm^2. The 1.0-sec peak photon flux measured starting from T0+4.3 s in the 10-1000 keV band is 4.3 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."