[vsnet-grb-info 18684] GRB 161104A: GROND observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20132
SUBJECT: GRB 161104A: GROND observations
DATE:    16/11/05 07:37:21 GMT
FROM:    Ana Nicuesa at TLS Tautenburg  <ana at tls-tautenburg.de>

A. Nicuesa Guelbenzu, S. Schmidl (both TLS Tautenburg) and J. Greiner
(MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 161104A (Swift trigger 720568; Mingo et
al., GCN 20123) 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 04:00 UT on 2016-11-05, 18 hours after the GRB
trigger. They were performed at an average seeing of 1" and at an
average airmass of 1.2.  Inside the enhanced 3.2" XRT position (GCN
20124, Goad et al.) we find a single source at coordinates:

Source A
RA (J2000.0) = 05:11:34.46
DEC (J2000.0) = -51:27:36.3
with an uncertainty of 0.5" in each coordinate.

At the border of the XRT error circle lie two more sources  at coordinates:

Source B
RA (J2000.0) = 05:11:34.31
DEC (J2000.0) = -51:27:33.6

Source C
RA (J2000.0) = 05:11:34.73
DEC (J2000.0) = -51:27:34.2

Their r'-band AB magnitudes are:

Source A
r' = 24.1 +- 0.1 mag,
Source B
r' = 24.3 +- 0.1 mag,
Source C
r' = 25.1 +- 0.3 mag,

For the moment no evidence for a fading of any of these objects can be
stated.

Given magnitudes are calibrated against GROND zeropoints and are not
corrected for the Galactic foreground extinction corresponding to a
reddening of E_(B-V) = 0.01 mag in the direction of the burst
(Schlafly & Finkbeiner 2011).

We thank Angela Hempel, La Silla, for performing the observations.