[vsnet-grb-info 18665] GRB 161023A: GROND Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20113
SUBJECT: GRB 161023A: GROND Observations
DATE:    16/10/25 06:37:38 GMT
FROM:    Thomas Kruehler at MPE Garching  <kruehler at mpe.mpg.de>

T. Kruehler and J. Greiner (both MPE Garching) report on behalf
of the GROND team:

We observed the field of GRB 161023A (INTEGRAL trigger 7613;
Mereghetti et al., GCN #20103) simultaneously in g'r'i'z'JHK with
GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG
telescope at the ESO La Silla Observatory (Chile).

Observations started at 23:52 UT on 2016-10-24, 25.2 hr after the GRB
trigger. They were performed at an average seeing of 1".6, and at an
average airmass of 1.1.

Based on combined images with 9.7 min of total exposures in g'r'i'z'
and 10.0 min in JHK at a mid-time of 00:12 UT on 2016-10-25,
we derive the following preliminary magnitudes (all in AB system) for
the optical/NIR afterglow (Gorbovskoy et al. GCN 20102, Tanvir et al.,
GCN 20104, Guidorzi et al., GCN 20107).

g' = 19.7 +- 0.1 mag
r' = 19.4 +- 0.1 mag
i' = 19.2 +- 0.1 mag
z' = 19.1 +- 0.1 mag
J = 18.7 +- 0.1 mag
H = 18.4 +- 0.1 mag
K = 18.2 +- 0.1 mag

Given magnitudes 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) = 0.03 mag
in the direction of the burst (Schlafly & Finkbeiner 2011).