TITLE:   GCN CIRCULAR
NUMBER:  9591
SUBJECT: GRB 090628: GROND upper limits
DATE:    09/06/29 09:05:28 GMT
FROM:    Thomas Kruehler at MPE/MPI  <kruehler@mpe.mpg.de>

T. Kruehler (MPE Garching), S. Klose (Tautenburg) and J. Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 090628 (Swift trigger #355942; Mangano et
al., GCN #9585) 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 La Silla
Observatory (Chile).

Observations started at 02:06 UT on June 29th, 2009, 4.8 hr after the
burst and were performed under poor seeing conditions. In stacked images
of 75 min total integration time in griz and 60 min in JHK, we do not
detect any object within the enhanced XRT error circle (Goad et al., GCN
#9590), down to the following limiting magnitudes (all in the AB system):

g' > 23.7
r' > 24.0
i' > 23.0
z' > 22.8
J > 21.8
H > 21.1
K > 20.5

These upper limits were derived using the GROND zeropoints and 2MASS field
stars as reference and are not corrected for the Galactic foreground
extinction corresponding to a reddening of E(B-V)=0.18 mag (Schlegel et
al., 1998).

We note the presence of a r'~23.5 mag source ~5 arcsec north east of the
center of the enhanced XRT error circle, which given the large offset is
very unlikely to be related to the GRB.