TITLE:   GCN CIRCULAR
NUMBER:  20848
SUBJECT: GRB 170311A: GROND upper limits
DATE:    17/03/11 15:45:09 GMT
FROM:    Patricia Schady at MPE/Swift  <pschady@mpe.mpg.de>

P. Schady and P. Wiseman (both MPE Garching) report:

We observed the field of GRB 170311A (Swift trigger 20846; Cummings et
al., GCN #20846) 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 09:45 UT on 2017-03-11, 1.6 hours after the GRB
trigger. They were performed at an average seeing of 1.2" and at an
average airmass of 1.1.

We do not detect a source within the Swift-XRT error circle (Cummings et
al., GCN #20846) down to the following 3 sigma limiting AB magnitudes:

g' > 23.1 mag
r' > 23.4 mag
i' > 22.7 mag
z' > 22.5 mag
J > 20.6 mag
H > 20.2 mag
K > 19.0 mag

The given limits are derived based on images calibrated against
Pan-STARRS/2MASS field stars, and are not corrected for the Galactic
foreground extinction corresponding to a reddening of E_(B-V)= 0.14 in the
direction of the burst (Schlafly & Finkbeiner 2011).