TITLE: GCN CIRCULAR NUMBER: 8296 SUBJECT: GRB 080928: GROND DETECTION DATE: 08/09/29 12:02:04 GMT FROM: Andrea Rossi at TLS Tautenburg A. Rossi (Tautenburg Obs.), C. Clemens, J. Greiner, A. Yoldas, T. Kruehler, R. Filgas (all MPE Garching), A. Kupcu Yoldas (ESO) and G. Szokoly (Eoetvoes Univ., Budapest) report on behalf of the GROND team: GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile), started observations of the field of GRB 080928 (Sakamoto et al. GCN #8292) in g'r'i'z'JHK at 04:46:00 UT on 2008-09-29, 13.5 hours after the burst trigger. We clearly detect the optical afterglow detected by UVOT (Sakamoto et al. GCN #8292) and ROTSE telescope (Rykoff et al. GCN #8293) in all optical bands, implying a redshift z<3.5. Observations continued for 90 min and were repeated at the mid-time 06:00 UT for a total 90 min. Both observations were done during strong wind and bad seeing (>2"). Calibrating the field on the SDSS standard SA95-149, we derive the following r' band observed magnitudes: midtime(s) r' err ------------------------ 50507 20.57 0.04 65807 21.36 0.06 Our data, when compared to the reported brightness of the afterglow reported by UVOT, suggest a break between the UVOT and the GROND measurements.