TITLE:   GCN CIRCULAR
NUMBER:  38702
SUBJECT: GRB 241228B: LCO optical observation
DATE:    24/12/29 03:35:55 GMT
FROM:    ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>

Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration.
 
We observed the field of the GRB 241228B triggered by Fermi (Fermi GBM team, GCN 38682) in B  filter of  the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring New South Wales, Australia. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel).
Observations began on December 28, 2024, starting from 10.97 hours after the GRB trigger.

We clearly detect the optical transient (OT) reported by GCNs (Kumar et al., GCN 38684 and GCN 38691, An et al. GCN 38687)  in our B band image. 

Date		UTstart	 	JD		 		t-T0 (hours)	Exp (sec)	Filter		Magnitude       
2024-12-28	15:11:37.24	2460673.13307			10.97		1 x 1200 	B		B = 21.35 +/- 0.03

The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.