[vsnet-grb-info 19969] GROND observations of GRB 171027A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22056
SUBJECT: GROND observations of GRB 171027A
DATE:    17/10/27 11:17:03 GMT
FROM:    Patricia Schady at MPE/Swift  <pschady at mpe.mpg.de>

P. Schady (MPE) reports:

Observations of the field of GRB 171027A (Swift trigger 783479; D'Avanzo
et al., GCN #22053) were carried out simultaneously in g'r'i'z' 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 08:51 UT on 27-10-2017, 28.4 mins after the GRB
trigger. They were performed during astronomical twilight, at an average
seeing of 1.4" and at an average airmass of 1.4.

Using a total exposure of 4.4 min, no source is detected within the 2.1"
enhanced Swift/XRT error circle (Evans et al., GCN 22054) down to the
following 3 sigma upper limits (all in AB):

g' > 23.1
r' > 23.1
i' > 22.3
z' > 22.2

Given magnitudes are calibration against PanSTARRS 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).

I acknowledge the excellent support provided by Angela Hempel in obtaining
these data.