GCN Circular 8296

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.