GCN Circular 11430

A. Nicuesa Guelbenzu, (Tautenburg Obs.), P.Schady and J.Greiner (MPE  
Garching) report on behalf of the GROND team:

We observed the field of GRB 101201A (Swift trigger 439595-6, Fermi  
GBM 312890511; Cummings et al., GCN #11429) 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 during twilight, at 00:36 UT on 2010-12-02, 14.6  
hours after the GRB trigger, and are continuing. They were performed  
at an average seeing of better than 0.8" and at an average airmass of 1.

We found a bright, uncatalogued point source within the 2 arcmin Swift- 
BAT error circle at

RA (J2000.0) = 00:07:52.19 s

DEC (J2000.0) = -16:11: 05.42

with an uncertainty of 0.5" in each coordinate.

The source is detected in all optical and NIR GROND filters and had a  
preliminary AB magnitude or r' = 19.67+/-0.01 10 mins after the start  
of our observations. The source faded by ~0.3 magnitudes within the  
first 1.5 hours of GROND observations, leading us to conclude that  
this is the afterglow of GRB101201A.

The detection of the source in the reddest GROND filter puts an upper  
limit on the redshift of this GRB of z < ~3. 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 mag in the direction of the burst (Schlegel et al.  
1998).