GCN Circular 18980

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

We observed the field of GRB 160203A (Swift trigger 672525; D'Avanzo et
al., GCN #18979) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla
Observatory (Chile).

Observations started at 02:18:58 UT on 2016-02-03, 6 min after the GRB
trigger, and are continuing. They were performed at an average seeing of
1".2 and at an average airmass of 1.8.

We found a single point source within the 2".3 Swift-XRT error circle at

RA (J2000.0) = 10:47:48.35
Dec. (J2000.0) = -24:47:19.8

with an uncertainty of 0".5 in each coordinate.

Based on the first 4.40 min of total exposures in g'r'i'z' and 4.0 min in
JHK at a mid-time of 02:22:14, we estimate preliminary magnitudes (all in
AB system) of

g' = 18.9 +/- 0.1 mag,
r' = 18.0 +/- 0.1 mag,
i' = 17.7 +/- 0.1 mag,
z' = 17.6 +/- 0.1 mag,
J  = 17.0 +/- 0.1 mag, and
H  = 16.7 +/- 0.1 mag.

While we cannot establish fading yet, we propose this source to be the
afterglow of GRB 160203A.

Given magnitudes are calibrated against GROND zeropoints as well as 2MASS
field stars and are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V) = 0.06 mag in the
direction of the burst (Schlafly & Finkbeiner 2011).