GCN Circular 18936

J. F. Graham, T. Schweyer, and J. Greiner (all MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 160123A (Swift trigger 671447; Malesani, et al., GCN # 18926) 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  04:02 UT on 25 Jan 2016, approximately 43 hours after the GRB trigger, and lasted for 2 hours. They were performed at an average seeing of 1.64" and at an average airmass of 1.06.

We do not detect a source within the Swift-XRT error circle reported by Beardmore et al. (GCN # 18927) down to (AB magnitudes)

g' > 24.1 mag,
r' > 24.4 mag,
i' > 24.0 mag,
z' > 23.9 mag,
J > 21.3 mag,
H > 20.9 mag, and
K > 20.1 mag.

The given limits are derived based on calibrating the images against GROND zeropoints and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.10 in the direction of the burst (Schlegel et al. 1998).