GCN Circular 8515
Subject
GRB 081109: GROND redshift limit and host extinction
Date
2008-11-10T19:25:43Z (16 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
C. Clemens, T. Kruehler, J. Greiner (all MPE Garching) report on
behalf of the GROND team:
We report on further analysis of the GROND data of GRB 081109 detected
by Swift (trigger 334112; Immler et al., GCN #8500) and Fermi/GBM
(von Kienlin 2008, GCN #8505) taken simultaneously in g'r'i'z'JHK.
In a combined 2~h exposure at a midtime of 18.5~hours after the burst,
we clearly detect the afterglow reported by D'Avanzo et al. (GCN
#8501) and Clemens et al. (GCN #8510) in all filters.
Using 2MASS field stars in JHK and the GROND zeropoints in g'r'i'z' we
estimate preliminary AB magnitudes of
g' = 23.14 +- 0.18 mag,
r' = 22.55 +- 0.15 mag,
i' = 22.00 +- 0.16 mag,
z' = 21.54 +- 0.15 mag,
J = 20.49 +- 0.07 mag,
H = 19.56 +- 0.06 mag and
K = 18.84 +- 0.10 mag
which have been corrected for the expected Galactic reddening of
E_(B-V)=0.02 (Schlegel et al. 1998).
Assuming Ly-alpha absorption, the g' band detection implies a redshift
of z < 3.5.
The Galactic foreground corrected broad band SED is best fit with a
power law template and significant extinction in the host. Depending
on the used model, the best fit intrinsic extinction A_V^{host}
varies between 0.6 and 1.2. We caution however, that this is strongly
dependent on the unknown redshift and subject to changes due to an
future improved calibration.