The bright optical flash from GRB 060117
  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. Later observations by other instruments set a strong limit on the optical and radio transient fluxes, unveiling an unexpectedly rapid further decay. We present an interpretation featuring a relatively steep electron-distribution parameter p ~ 3.0 and providing a straightforward solution for the overall fast decay of this optical transient as a transition between reverse and forward shock. 
Martin Jel\'inek, Michael Prouza, Petr Kub\'anek, Ren\'e Hudec, Martin   Nekola, Jan \v{R}\'idk\'y, Ji\v{r}\'i Grygar, Marti...