GCN Circular 18680

P. Wiseman, T. Kruehler (both MPE Garching), D. A. Kann (TLS
Tautenburg), C. Delvaux, and J. Greiner (both MPE Garching) report on
behalf of the GROND team:

We observed the field of GRB 151210A (Swift trigger 666931; Evans et
al., GCN #18678) simultaneously in g'r'i'z'JHK with GROND (Greiner et
al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La
Silla Observatory (Chile).

Observations started at 03:17:35 UT on 10/12/2015, 279 sec after the
GRB trigger, and are ongoing.

We detect a source not seen in the DSS at the edge of the refined XRT
error circle (Evans et al., GCN #18678) at:

RA (J2000) = 04:20:27.91
Dec. (J2000) = -71:15:02.6

with an error of 0".5 in each coordinate. We suggest that this is the
afterglow of the GRB, as we also detect fading between observations. This
source is also seen by LCOGT (Han et al., GCN #18679).

Based on observations with an integration time of 594 sec (griz) and
540 sec (JHK) centered 54 min after the GRB trigger, we derive
magnitudes

g' = 23.9 +/- 0.2  mag,
r' = 22.1 +/- 0.1 mag,
i' = 21.7 +/- 0.1 mag,
z' = 21.2 +/- 0.1 mag,
J = 20.3 +/- 0.2 mag, and
H = 19.8 +/- 0.2 mag.

The given limits are derived based on calibrating the images against
GROND zero points and 2MASS field stars and are not corrected for the
Galactic foreground extinction corresponding to a reddening of E_(B-
V)= 0.11 in the direction of the burst (Schlafly & Finkbeiner 2011).