[vsnet-grb-info 14318] GRB 131227A: GROND Upper Limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15632
SUBJECT: GRB 131227A: GROND Upper Limits
DATE:    13/12/29 17:07:39 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann at tls-tautenburg.de>

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

We observed the field of GRB 131227A (Swift trigger 582184; Oates et al.,
GCN 15616) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2m MPG telescope at La Silla Observatory
(Chile).

Observations started at 02:10 UT on December 28th, around 21.4 hrs after
the GRB trigger, and lasted for 2 hours. They were performed at an average
seeing of 1".0 and at an average airmass of 2.

At the position of the optical afterglow reported by Zheng et al. (GCN
15617) and Cucchiara et al. (priv. comm., see also GCN 15624) we do not
detect any source down to 3-sigma AB limiting magnitudes of

g' > 25.7,
r' > 25.6,
i' > 24.8,
z' > 24.6,
J > 21.8,
H > 21.1, and
K > 19.7.

We do detect a compact source to the north-east, at

RA (J2000) = 04:29:30.90
Dec. (J2000) = +28:53:00.3

with an uncertainty of 0".3 and AB magnitudes

r' = 24.28 +/- 0.1,
i' = 24.19 +/- 0.1,
z' = 22.82 +/- 0.1, and
J  = 20.66 +/- 0.4.

It is undetected to above-mentioned limits in the other filters. The
relationship of this source to the afterglow is unclear.

The given limits and magnitudes are derived based on calibrating the
images against GROND zeropoints in g'r'i'z' and 2MASS field stars in JHK
and are not corrected for the Galactic foreground extinction corresponding
to a reddening of E_(B-V)= 1.02 mag in the direction of the burst
(Schlegel et al. 1998).