TITLE:   GCN CIRCULAR
NUMBER:  38733
SUBJECT: GRB 241228B: SAO RAS optical observations
DATE:    24/12/30 21:08:56 GMT
FROM:    Moskvitin Alexander at SAO RAS <mosk@sao.ru>

A. S. Moskvitin, O. I. Spiridonova, Yu. V. Sotnikova (SAO RAS), 
A. Volnova, A. Pozanenko (IKI), A. Ghosh, S. Razzaque (CAPP, 
University of Johannesburg), report on behalf of the GRB follow-up team.

We observed the field of GRB 241228B discovered by Fermi (Fermi GBM 
team, GCN 38682; Scotton and Meegan, GCN 38714), Swift (Evans, 
GCN 38688; Burrows et al., GCN 38713) with the 1-m telescope of SAO RAS
Zeiss-1000 equipped with the CCD-photometer on December 29, 21:49:11 -- 
22:57:57 UT (t_mid - T0 = 1.7573 days). We obtained 12 x 300 sec. 
images in Rc band.

The GOTO24jmz optical counterpart (Kumar et al., GCN 38684, GCN 38691; 
An et al. GCN 38687; Ortega-Casas et al., GCN 38692; Ghosh et al., 
GCN 38702; An et al., GCN 38704; Volnova et al., GCN 38709; 
Strobl and Jelinek, GCN 38715) is clearly detected in the stacked image 
with the brightness of R = 20.97 +/- 0.06. Based on photometry in R 
filter (this report and photometry by Volnova et al., GCN 38709) 
we found that the light curve of the afterglow of GRB 241228B/GOTO24jmz 
can be fitted with a simple power-law model 
with an power law index of -0.66.

The photometry is based on nearby SDSS stars used by Volnova et al., 
GCN 38709 (magnitudes were converted with Lupton 2005 equations).