TITLE: GCN CIRCULAR NUMBER: 8745 SUBJECT: GRB 081228: detection by GROND DATE: 08/12/28 07:50:22 GMT FROM: Paulo M. J. Afonso at MPE GRB 081228: detection by GROND P. Afonso (MPE), S. Klose (Tautenburg), T. Kruehler, (MPE), J. Greiner (MPE), A. Updike (Clemson University), A. Kupcu-Yoldas(ESO), A. Yoldas (MPE), and G. Szokoly (Eötvös 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) imaged the field of GRB 081228 (Swift trigger 338338, Page et al., GCN #8742) simultaneously in g'r'i'z'JHK. Inside the enhanced XRT error circle (position, RA (J2000): 02h 37m 50.77s Dec (J2000): +30d 51' 09.5"), reported by Goad et alia, GCN #8744, we detect an object in the g'r'i'z' bands, but not in JHK. Observations started at 01h26 UT, 9 min after the burst. We used 4 images of 375 s exposure in g'r'i'z' and 120 images of 10s exposure in JHK. The images midtimes for g'r'i'z' and JHK are respectively 02h23m59s and 02h24m20s UT, or 1h6m19s and 1h6m40s after the burst. Observations were done at high air mass and seeing bigger than 1''. The object is detected in the g'r'i'z' bands, implying a redshift smaller than 3.5. The detection is fainter in the g' band. Preliminary VEGA magnitudes calibrated against USNO-B field stars and upper limits are as follows: g' = 23.73 +/- 0.11 r' = 21.98 +/- 0.04 i' = 21.42 +/- 0.06 z' = 21.80 +/- 0.08 J > 19.6 H > 18.4 K > 17.6 No correction for galactic extinction was done.