The RAPid Telescopes for Optical Response ( RAPTOR ) system at Los Alamos National Laboratory observed GRB 060206 starting 48.1 minutes after \gamma -ray emission triggered the Burst Alert Telescope ( BAT ) on-board the Swift satellite .
The afterglow light curve measured by RAPTOR shows a spectacular re-brightening by \sim 1 mag about 1 h after the trigger and peaks at R \sim 16.4 mag .
Shortly after the onset of the explosive re-brightening the OT doubled its flux on a time-scale of about 4 minutes .
The total R -band fluence received from GRB 060206 during this episode is 2.3 \times 10 ^ { -9 } erg cm ^ { -2 } .
In the rest frame of the burst ( z = 4.045 ) this yields an isotropic equivalent energy release of E _ { iso } \sim 0.7 \times 10 ^ { 50 } erg in just a narrow UV band \lambda \simeq 130 \pm 22 nm .
We discuss the implications of RAPTOR observations for untriggered searches for fast optical transients and studies of GRB environments at high redshift .