TITLE:   GCN CIRCULAR
NUMBER:  19396
SUBJECT: GRB 160506A: GROND upper limits
DATE:    16/05/06 09:12:52 GMT
FROM:    Fabian Knust at MPE/GROND  <fknust@mpe.mpg.de>

F. Knust, C. Delvaux, J. Greiner (all MPE Garching) report on behalf of
the GROND team:

We observed the field of GRB 160506A (Swift trigger 685245; Hagen et al.,
GCN #19394) 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  06:45 UT on 2016-05-06, 3.25 hrs after the GRB
trigger. They were performed through substantial cirrus at an average
seeing of 2.1" and at an average airmass of 1.1.

We do not detect any source within the Swift-XRT error circle reported by
Osborne et al. (GCN #19395) down to

g' > 20.9 mag,
r' > 22.1 mag,
i' > 21.5 mag,
z' > 21.7 mag,
J > 19.4 mag,
H > 19.1 mag, and
K > 17.2 mag.
(all in AB),

but we see two faint sources north-east and sout-west of the XRT error
circle, each about 4 arcsec away from the XRT centroid.

Given magnitudes are calibrated against USNO as well as 2MASS field stars
and are not corrected for the expected Galactic foreground extinction
corresponding to a reddening of E_(B-V)=0.26 mag in the direction of the
burst (Schlegel et al. 1998).