TITLE:   GCN CIRCULAR
NUMBER:  18902
SUBJECT: GRB 160119A: GROND optical/NIR afterglow observations
DATE:    16/01/19 18:52:32 GMT
FROM:    Ting-Wan Chen at MPE  <jchen@mpe.mpg.de>

T.-W. Chen, T. Kruehler, F. Knust, J. Greiner (all MPE Garching), and D. A. Kann (TLS Tautenburg) report on behalf of the GROND team:

We observed the field of GRB 160119A (Swift trigger 671014; Marshall et al., GCN #18893) 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 07:53 UT on 2016-01-19, about 4.8 hours after the GRB trigger. 

Our images were performed at an average seeing of 1.8" and at an average airmass of 2.0. Based on 19 min of total exposure in g'r'i'z' and 16 min in JHK at a midtime of 08:38 UT on 2016-01-19, we estimate the detection and upper-limit magnitudes (all in the AB system):

g' > 23.9 mag,
r' = 23.6 +- 0.2 mag,
i' = 22.9 +- 0.2 mag,
z' = 22.5 +- 0.2 mag,
J > 20.5 mag,
H > 20.2 mag, and
K > 19.1 mag.

Our observation was about 4.8 hours later than the NOT followup observed by Malesani et al. (GCN #18895), and about 0.2 hours earlier than the RATIR observation by Cucchiara et al. (GCN #18901).
The fading of r'-band magnitudes between NOT and GROND is about 0.85 mag, and within the uncertainties between GROND and RATIR. The decline rate is about 0.18 mag/hr, which confirms the afterglow nature.

The given magnitudes are derived based on calibrating the images against SDSS and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E(B-V)= 0.03 mag in the direction of the burst (Schlafly & Finkbeiner 2011).