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GCN Circular 10286

Subject
GRB 091221, GROND observations
Date
2009-12-22T03:20:01Z (14 years ago)
From
Sylvio Klose at TLS Tautenburg <klose@tls-tautenburg.de>
R. Filgas, P. Afonso (both MPE Garching), S. Klose (TLS Tautenburg), and 
J. Greiner (MPE Garching), report on behalf of the GROND team:

GROND (Greiner et al. 2008, PASP 120, 405), the 7-channel imager mounted 
at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile), started 
follow-up observations of GRB 091221 (Krimm et al. 2009, GCN 10283) on Dec 
22, at 01:27 UT (4.5 hrs after the burst).

For the suggested GRB afterglow (Zheng et al. 2009, GCN 10284; Holland et 
al. 2009, GCN 10285), based on a first 8 min exposure, we estimate the 
following preliminary magnitudes (in the AB system):

g' = 22.90 +/- 0.30
r' = 22.27 +/- 0.30
i' = 21.95 +/- 0.30
z' = 22.20 +/- 0.30
J  = 20.16 +/- 0.20
H  > 19.9
K  > 19.1

using GROND zeropoints and 2MASS catalog (airmass 1.8). Observations are 
ongoing.

Taking into account a Galactic reddening of E(B-V)=0.22 mag (Holland et 
al. 2009, GCN 10285), we estimate a photometric redshift of z<3.5. At 
present we cannot decide if the z'-band magnitude is indicating to a 
broad-band absorption feature or if we underestimate the magnitude error
in this band (where the source is very faint).
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