R-band photometry of GRB 060206

The afterglow light curve measured by RAPTOR shows a spectacular rebrightening by ~1mag about 1hr after the trigger and peaks at R~16.4mag. Shortly after the onset of the explosive rebrightening, the optical transient doubled its flux on a timescale of about 4min.

The total R-band fluence received from GRB 060206 during this episode is 2.3x10^9^ergs/cm^2^. In the rest frame of the burst (z=4.045), this yields an isotropic equivalent energy release of E_iso_~0.7x10^50^ergs in just a narrow UV band, {lambda}~130{+/-}22nm. We discuss the implications of RAPTOR observations for untriggered searches for fast optical transients and studies of GRB environments at high redshift.