GRB 060117: Reverse + forward shock solution

Abstract

We present a discovery and observation of an extraordinarily bright prompt optical emission of the GRB 060117 obtained by a wide-field camera atop the robotic telescope FRAM of the Pierre Auger Observatory from 2 to 10 minutes after the GRB. We found rapid average temporal flux decay of alpha = -1.7 +/- 0.1 and a peak brightness R = 10.1 mag. We interpret the shape of the lightcurve as a transition between reverse and forward shock emission.