[vsnet-grb-info 8786] GRB 091221, GROND observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10286
SUBJECT: GRB 091221, GROND observations
DATE:    09/12/22 03:20:01 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose at 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).