TITLE: GCN CIRCULAR NUMBER: 7834 SUBJECT: GRB 080605: GROND detection of the optical afterglow candidate DATE: 08/06/06 04:30:38 GMT FROM: Christian Clemens at MPE C. Clemens, T. Kruehler, J. Greiner, A. Kupcu Yoldas, A. Yoldas (all MPE Garching) and G. Szokoly (Eoetvoes Univ., Budapest and MPE Garching) report on behalf of the GROND team: We observed the field of GRB 080605 (Swift trigger 313299; Sbarufatti et al., GCN #7828) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile). Observations started at 01:10:59 UT on June 6th, 2008, 83 mins after the GRB trigger, and are continuing. We found a single and relatively bright point source within the 1.0'' Swift-UVOT error circle reported by Holland et al. (GCN #7830) at RA (J2000.0) = 17h 28m 30.05s DEC (J2000.0) = +04d 00' 56.2" with a typical uncertainty of 0.8", which is consistent with the sources reported by Kann et al. (GCN #7829) and Gomboc et al. (GCN #7831). Based on 460 s and 1500 s of effective exposures taken 1.65 hrs and 2.78 hrs after the trigger, we estimate preliminary magnitudes of r' = 20.3 and i' = 19.4, as well as r' = 20.7 and i' = 19.9 with typical errors of +/- 0.1. (Given magnitudes are calibrated against USNO-B1 field stars and might be affected by the bright, nearby star.) This indicates a clear fading of the source, which we therefore suggest to be the optical afterglow of GRB 080605.