GCN Circular 8510
Subject
GRB 081109: GROND Detection of the Optical/NIR Afterglow Candidate
Date
2008-11-10T03:34:52Z (16 years ago)
From
Christian Clemens at MPE <cclemens@mpe.mpg.de>
C. Clemens, T. Kruehler, J. Greiner (all MPE Garching) and G. Szokoly
(Eoetvoes Univ., Budapest and MPE) report on behalf of the GROND team:
We observed the field of GRB 081109 (Swift trigger #334112; Immler et al., GCN
#8500) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP
120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla Observatory
(Chile).
Observations started at 00:08 UT on November 10th, 2008, 17.1 hr after the GRB
trigger, and are continuing. They were performed during astronomical twilight
at an average seeing of 1.0" and at an average airmass of 1.1 as well as
under bright Moon.
Based on the first 7.7 min of total exposures in g'r'i'z' and 8.0 min in JHK,
we detect the afterglow candidate reported by D'Avanzo et al. (GCN #8501) and
estimate preliminary magnitudes (all in AB system) of
g' > 22.8
r' ~ 22.8 +/- 0.3
i' ~ 21.8 +/- 0.15
z' ~ 21.4 +/- 0.15
J ~ 20.4 +/- 0.10
H ~ 19.7 +/- 0.15
K ~ 18.9 +/- 0.20
These magnitudes are calibrated against GROND zeropoints as well as
2MASS field stars.
The spectral energy distribution is very red, and requires an extinction
of A_V > 0.5. With this strong extinction, and our g'-band limit being
compromised by the nearby full Moon, we cannot derive a redshift
at this stage.