GCN Circular 10815

P. Afonso (MPE Garching), A. Nicuesa, A. Rossi, S. Klose (TLS Tautenburg),
T. Kruehler, A. Yoldas and J. Greiner (MPE Garching), report on behalf 
of the GROND team:

We observed the field of GRB 100528A discovered by SuperAGILE (Del Monte et
al., GCN #10810) and observed also by Fermi/GBM (Rau & van der Horst, 
GCN #10811),
simultaneously in g'r'i'z'JHK with GROND (Greiner et al.2008, PASP 120, 
405)
mounted at the 2.2 m MPI/ESO telescope at La Silla Observatory (Chile).

Observations started at 07:49 UT on March 30, 54 hours after the GRB
trigger. At the position of the UVOT detection (Grupe et al., GCN #10813)
we detect and confirm the afterglow mentioned also by Xu et al. (GCN 
#10814).

Based on stacked images with a total integration time of 40 minutes in 
JHK and
50 minutes in g'r'i'z' we estimate the following preliminary magnitudes
(all in the AB system):

g' = 21.93+-0.08
r' = 21.56+-0.04
i' = 21.27+-0.05
z' = 21.36+-0.07
J  = 20.49+-0.10
H  = 20.25+-0.12
K  = 20.46+-0.21

All magnitudes given above are calibrated against SDSS and 2MASS field 
stars.
No correction has been applied for the large, uncertain Galactic foreground
extinction corresponding to a reddening of E(B-V)~ 0.22 in the direction
of the burst (Schlegel et al. 1998).