TITLE:   GCN CIRCULAR
NUMBER:  18219
SUBJECT: GRB 150831A: GROND Upper Limits
DATE:    15/09/01 03:00:06 GMT
FROM:    Fabian Knust at MPE/GROND  <fknust@mpe.mpg.de>

F. Knust (MPE Garching), S. Klose (TLS Tautenburg), and J. Greiner (MPE Garching) report on behalf of the GROND team: 
We observed the field of GRB 150831A (Swift trigger 653838; Lien et al., GCN #18209) simultaneously in g'r'i'z'JHK 
with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). 
Observations started at 23:21UT on 2015-08-31, 13hrs after the GRB trigger. They were performed at
an average seeing of 2.4" and at an average airmass of 1.5. 

We do not detect a source within the Swift-XRT error circle reported by Osborne et al. (GCN #18212) down to 
g'> 24.9 mag, 
r'> 24.5 mag, 
i'> 23.8 mag, 
z'> 23.8 mag, 
J> 21.4 mag, 
H> 20.9 mag, and 
K> 18.6 mag. 

The given limits are derived based on calibrating the images against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.1 mag in the direction of the burst (Schlegel et al. 1998).