GCN Circular 23516

P. Schady (Univ. of Bath) and J. Bolmer (MPE, Garching) report:

We observed the field of GRB 181203A (Swift trigger 874475; Troja et al., GCN #23493) 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 02:02 UT on 4th December, 13.4 hours after the GRB trigger. They were performed
at an average seeing of 1.6" and at an average airmass of 1.4. 

We found a faint source within the 2.0 arcsec Swift-XRT error circle reported by Goad et al. (GCN #23494) at

RA (J2000.0) = 07:13:23.705
DEC (J2000.0) = -39:48:05.29

with an uncertainty of 0.12" in each coordinate. The source is detected in all filters apart from the z' band,
and has a preliminary r'-band AB magnitude of 

r' = 23.5 +/- 0.1 mag

The above magnitude is calibrated against GROND zeropoints and is not corrected for the expected
Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.21 in the direction of the
burst (Schlafly & Finkbeiner 2011).

We thank Angela Hempel for the excellent support from La Silla.