[vsnet-grb-info 16916] GRB 150821A: LCOGT Sutherland observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18197
SUBJECT: GRB 150821A: LCOGT Sutherland observations
DATE:    15/08/23 11:56:57 GMT
FROM:    Cristiano Guidorzi at Ferrara U,Italy  <guidorzi at fe.infn.it>

C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), A. Gomboc (U. Ljubljana), 
C. Mundell (U. Bath) on behalf of a larger collaboration report:

The 1-m LCOGT telescopes in Sutherland (South Africa) began observing 
Swift GRB 150821A (Troja et al. GCN 18186) on August 21, 19:39 UT (~9.9 
hours after the burst trigger) with SDSS r and i filters.
At the position of the optical afterglow (Troja et al. GCN 18186; D'Elia 
et al. GCN 18187; Kuin et al. GCN 18192; Kruehler et al. GCN 18195) we 
do not detect any source down to the following limits:

Mid Time      Exposure       Filter       Magnitude
(hrs)           (s)
---------------------------------------------------
10.4           2880          r'           > 20.4
10.6           2880          i'           > 21.0
---------------------------------------------------

Calibration is done against R2 and I values of USNOB-1 nearby stars.