[vsnet-grb-info 16918] GRB 150821A: LCOGT Siding Springs early observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18199
SUBJECT: GRB 150821A: LCOGT Siding Springs early observations
DATE:    15/08/24 15:29:32 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 Siding Springs (Australia) began observing 
Swift GRB 150821A (Troja et al. GCN 18186) on August 21, 10:22 UT (38 
minutes after the burst trigger) with SDSS r and i filters under 
initially poor sky conditions.
We detect the optical afterglow (Troja et al. GCN 18186; D'Elia et al. 
GCN 18187; Kuin et al. GCN 18192; Kruehler et al. GCN 18195) with the 
following magnitudes:

Mid Time      Exposure       Filter       Magnitude
(min)           (s)
-----------------------------------------------------
135           1680          r'           19.1 +- 0.4
233            480          r'           19.7 +- 0.3
398            720          r'           20.3 +- 0.2
-----------------------------------------------------

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