TITLE:   GCN CIRCULAR
NUMBER:  8266
SUBJECT: GRB 080916A: GROND lightcurve
DATE:    08/09/18 11:23:16 GMT
FROM:    Andrea Rossi at TLS Tautenburg  <rossi@tls-tautenburg.de>

A. Rossi (Tautenburg Obs.),T. Kruehler, J. Greiner, A. Yoldas, C. Clemens,
 R. Filgas (all MPE Garching), A. Kupcu Yoldas (ESO) and 
G. Szokoly (Eoetvoes Univ.,Budapest) report on behalf of the GROND team:

GROND (Greiner et al. 2008, PASP 120, 405),  mounted at the 2.2m ESO/MPI
telescope at La Silla Observatory (Chile), started observations of the
field of GRB 080916A (Ziaeepour et al. GCN #8237) in g'r'i'z'JHK at 
23:57:34 UT on 2008-09-16, 14 hours after the burst trigger.

We clearly detect the optical afterglow detected by UVOT (Ziaeepour 
et al. GCN #8237) and REM telescope (Fugazza et al. GCN #8238). 
Observations continued for 60 min and were repeated at the mid-time 
06:40 UT for total 60 min.

Calibrating the field on USNO-B1 stars, we derive the following
r band magnitudes, not corrected for the Galactic foreground 
extinction corresponding to a reddening of E_(B-V)=0.019 mag 
(Schlegel et al. 1998):

midtime(s)	r	er
52239       	21.8	0.03
54054       	21.9	0.04
74076       	22.1	0.07
76260        	22.3	0.07

The total r band light curve is well fitted by power law with index 
of 0.81+- 0.13. Assuming the optical light curve continues 
the decline with the same power law index, we predict r' 
band magnitudes 23.4 at 3 days after the burst.