TITLE: GCN CIRCULAR NUMBER: 14795 SUBJECT: GRB 130606B: Fermi-LAT detection of a bright hard burst DATE: 13/06/07 01:20:12 GMT FROM: Giacomo Vianello at SLAC G. Vianello (Stanford University), J. Racusin (NASA/GSFC), Nicola Omodei (Stanford University) and M. Ohno (Hiroshima U.) report on behalf of the Fermi-LAT team: At 11:55:33 UT on 06 June 2013, Fermi LAT detected high energy emission from GRB 130606B, which was also detected by Fermi-GBM (trigger 392212536 / 130606497). The brightness of the event in GBM triggered an autonomous repoint of the spacecraft. Unfortunately, the GBM flight software determined an unreliable position and the spacecraft slewed to that position. We were nevertheless able to detect a very clear excess at the position: (RA, Dec) = 218.574, -22.131 (J2000) with an error radius of 0.1 deg (68% containment radius, statistical errors only) which was within the LAT field of view between T0 + 180 s and T0 + 1000 s. Using SOURCE class we detected > 10 events, with 4 events above 1 GeV, compatible with the position of the source during this time interval. This source was about 91 deg from the LAT boresight at the time of the trigger and during the whole prompt emission (~100 s long), well outside the nominal field of view for the standard data analysis. However, we detected a strong signal using the non-standard LLE selection, most sensitive in the 10 MeV - 100 MeV energy range and featuring a broader acceptance. We detected an excess of more than 17 sigma in a time interval from 5 to 30 s after the trigger, composed of few hundreds events above the background level. The effective area of the LLE class is small at such high off-axis angle, therefore the strong excess indicates that this burst was exceptionally bright and hard. A Swift TOO request has been submitted. A GBM circular is forthcoming. The Fermi LAT point of contact for this burst is Giacomo Vianello ( giacomov@stanford.edu). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. -- ----------------------------------------------------------- Giacomo Vianello Stanford University, Hansen Experimental Physics Lab, 452 Lomita Mall, Stanford, CA 94305-4085 "A few observation and much reasoning lead to error; many observations and a little reasoning to truth." (A.Carrell) ICQ: 566213964 -----------------------------------------------------------