[vsnet-grb-info 16914] GRB 150821A: GROND afterglow observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18195
SUBJECT: GRB 150821A: GROND afterglow observations
DATE:    15/08/22 04:11:28 GMT
FROM:    Thomas Kruehler at MPE Garching  <kruehler at mpe.mpg.de>

T. Kruehler (ESO), F. Schrey, W. Bornemann, A. Rau and J. Greiner
(all MPE)  report on behalf of a larger collaboration:

We observed the field of GRB 150821A (Swift trigger 652847;
Troja et al., GCN 18186) 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 02:02 UT on 2015-08-22, 16.3 hours after the
GRB trigger. For the optical afterglow (Troja et al., GCN 18186,
D'Elia et al. GCN 18187, Kuin & Troja, GCN 18192) we derive magnitudes of:

g = 23.2 +- 0.1
r = 22.6 +- 0.1
i = 22.3 +- 0.1
z = 22.0 +- 0.2

at a midtime of 17.0 hours after the trigger. This photometry is in the
AB system and calibrated against GROND zeropoints. Because GROND is 
presently being recommissioned, our measurements are preliminary.