GCN Circular 9862
F. Olivares, T. Kruehler and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 090831C (Swift trigger #361489; Schady et al., GCN #9854) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at LaSilla Observatory (Chile). Observations started at 08:07 UT on September 1st, 2009, 10.6 hr after the burst. At this time the position of the burst was becoming visible above the pointing constraints of the telescope. Observations suffer from high airmass and large seeing of around 2". In stacked images of 74 min total integration time in griz and 60 min in JHK, we do not detect any object within the enhanced XRT error circle (Evans et al., GCN #9855), down to the following limiting magnitudes (all in the AB system): g' > 23.5 r' > 24.0 i' > 23.3 z' > 22.9 J > 21.4 H > 21.1 K > 20.0 These upper limits were derived using the GROND zeropoints and 2MASS field stars as reference and are not corrected for significant Galactic foreground extinction corresponding to a reddening of E(B-V)=0.38 mag (Schlegel et al., 1998).