TITLE:   GCN CIRCULAR
NUMBER:  11091
SUBJECT: GRB 100814A: GROND Detection of the Optical/NIR Afterglow 
DATE:    10/08/14 11:20:51 GMT
FROM:    Patricia Schady at MPE/Swift  <pschady@mpe.mpg.de>

R. Filgas, P. Schady and J. Greiner (MPE Garching) report on behalf of  
the GROND team:


We observed the field of GRB 100814A (Swift trigger 431605; Beardmore  
et al., GCN #11087) simultaneously in g'r'i'z'JHK with GROND (Greiner  
et al. 2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at  
La Silla Observatory (Chile).

Observations started at 03:57 UT, 7 minutes after the GRB trigger at  
03:50 UT, and are continuing. They were performed at an average seeing  
of 1.2" and at an average airmass of 2.

We detect a single point source in all GROND optical (g'r'i'z') and  
NIR bands (JHK) at a position consistent with the coordinates provided  
by Schaefer et al. (GCN #11086) and Gronwall et al. (GCN #11088), and  
consistent with the spectroscopic redshift of z=1.44 (O'Meara et al.  
GCN #11089).

The afterglow decays as a power law with a best-fit index of alpha ~  
0.5, decaying from r' = 18.0 +/- 0.1 at T+25 minutes down to r' = 19.5  
+/- 0.1 (all in AB system) by the end of our observations, at T+6  
hours. Analysis is on going.

Given magnitudes are calibrated against USNO zeropoints and are not  
corrected for the expected Galactic foreground extinction  
corresponding to a reddening of E(B-V)=0.02 in the direction of the  
burst (Schlegel et al. 1998).