A. C. Updike (NASA/GSFC), P. Schady, J. Greiner (both MPE Garching),
T. Kruehler (DARK/NBI), D. A. Kann, S. Klose and A. Rossi (all TLS
Tautenburg) report on behalf of the GROND team:
We observed the field of GRB 110715A (Swift trigger 457330; Sonbas et
al., GCN #12158) 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 00:35 UT on 18th July, lasting just under 2hrs
and with a midtime ~3dys after the GRB trigger. They were performed at
an average seeing of 1.1" and at an average airmass of 1.
We found a single point source within the 2.2" Swift-XRT error circle
reported by Evans et al. (GCN #12161), consistent with the UVOT
position (Kuin et al., GCN #12162).
Based on 4136s of total exposures in g'r'i'z' and 4320s in JHK, we
estimate preliminary magnitudes (all AB system) of
g' = 22.59 +/- 0.09
r' = 21.22 +/- 0.02
i' = 20.53 +/- 0.02
z' = 19.93 +/- 0.02
J = 19.56 +/- 0.24
H = 18.79 +/- 0.17
K = 18.86 +/- 0.31
Given optical and NIR magnitudes are calibrated against GROND
zeropoints and 2MASS field stars, respectively, and are not corrected
for the expected Galactic foreground extinction corresponding to a
reddening of E(B-V)=0.60 mag in the direction of the burst (Schlegel
et al. 1998).