GCN Circular 12403
Subject
GRB 110825A: GROND Observations
Date
2011-09-28T13:13:39Z (13 years ago)
From
Vladimir Sudilovsky at MPE <vsudilov@mpe.mpg.de>
V. Sudilovsky, J. Greiner, A. Rau (All MPE Garching), and S. Klose (TLS
Tautenburg) report on behalf of the GROND team:
We observed the field of the IPN GRB 110825A (Hurley et al., GCN 12307)
on 2011 August 29 at 08:55 UT (52hr post trigger) simultaneously in
g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at
the 2.2m MPI/ESO telescope at La Silla Observatory (Chile).
With an exposure time of 3000s we do not find any source within the XRT
error circle (Zhang et al., GCN 12308). In particular, the object
reported by Xu et al. (GCN 12311) is not detected with a 3-sigma
limiting magnitude of r' ~ 24.5 calibrated against USNO B1. This is
consistent with the non-detection reported by Zhao et al (GCN 12314) and
suggests that the source must have faded by at least 0.9mag within the
first 48hr after the trigger. The optical decline is in agreement with a
similar decay by a factor of 3 seen in the XRT lightcurve between day 1
and day 5 (Zhang et al., GCN 12334). While this could suggest the source
detected by Xu et al. to be the afterglow of GRB110825A, the very late
re-brightening observed in X-rays (Zhang et al., GCN 12334) makes this
interpretation unlikely.
Further deep optical imaging and X-ray monitoring are encouraged to
resolve the nature of this source.
We thank Kim Page and Phil Evans for providing helpful details
concerning the XRT observations of GRB 110825A.