TITLE:   GCN CIRCULAR
NUMBER:  37344
SUBJECT: GRB 240828A: SAO RAS optical observations
DATE:    24/08/29 21:25:40 GMT
FROM:    Moskvitin Alexander at SAO RAS <mosk@sao.ru>

A. S. Moskvitin and O. I. Spiridonova (SAO RAS)
report on behalf of the GRB follow-up team.

We observed the field of GRB 240828A (Fermi GBM team, GCN 37317;
Srijan et al., GCN 37328; Gupta and Di Lalla, GCN 37331;
Beardmore et al., GCN 37337; Dalessi and Meegan GCN 37341)
with the SAO RAS 1-meter telescope Zeiss-1000 equipped with
the CCD-photometer. We obtained 3 x 300 sec frames in each of BVRcIc
filters on August 29.

The OT (Zheng and Filippenko; GCN 37339) is clearly detected in our
images. The results are as follows.

Start    -- Stop, UT  t_mid - T0, d   filter  mag +/- err
18:14:38 -- 18:33:37  1.14515         B       20.54 +/- 0.05
18:34:12 -- 18:50:59  1.15798         V       20.16 +/- 0.05
17:38:50 -- 17:56:05  1.11969         Rc      19.73 +/- 0.03
17:56:52 -- 18:13:53  1.13213         Ic      19.36 +/- 0.07

Magnitudes were calibrated against nearby SDSS stars (converted with
Lupton 2005 equations) and not corrected for the MW extinction.