P. Wiseman, F. Knust, J. Greiner (all MPE Garching) report on behalf of
the GROND team:
We observed the field of GRB 160220A (Swift trigger 674670; Lien et al.,
GCN #19023) 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
Observations started at 05:46 UT on 2016-02-20, 4.5 hrs after the GRB
trigger. They were performed at an average seeing of 1.5" and at an
average airmass of 1.6.
We do not find any single point source within the 1.9" Enhanced Swift-XRT
error circle reported by Evans et al. (GCN #19025). Based on 36.00 min of
total exposures in g'r'i'z' and 30.00 min in JHK, at a mid-time of 06:49
UT, we estimate preliminary upper limiting magnitudes (AB system) of
g' > 23.4 mag,
r' > 23.9 mag,
i' > 23.6 mag,
z' > 23.3 mag,
J > 21.6 mag,
H > 20.9 mag, and
K > 18.0 mag.
Given limits 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)=0.12 mag in the
direction of the burst (Schlafly & Finkbeiner 2011).