TITLE:   GCN CIRCULAR
NUMBER:  42545
SUBJECT: GRB 251103A: LCO optical observation
DATE:    25/11/03 11:02:49 GMT
FROM:    ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>

Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg),  Rahul Gupta (NASA GSFC),  Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration. 

We observed the field of the GRB 251103A triggered by SVOM/ECLAIRs (Hu et al., GCN 42534) in V and r  filters of  the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at McDonald Observatory. 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 November 03, 2025, starting from 4.22 hours after the GRB trigger.

We clearly detect the optical transient (OT) reported by GCNs (Schneider et al., GCN 42535; Turpin et al., GCN 42538; Gritsevich et al., GCN 42539; Izzo et al., GCN 42540, O'Neill et al., GCN 42543) in our V and r band images. 

|Date|		|JD start|		|t-T0 (hours)|	|Exp (sec)|	|Filter|   |Magnitude|  
-----------------------------------------------------------------------------------------------------     
2025-11-03	2460982.90068		4.226		1 x 500 	V	   V = 19.38 +/- 0.08
2025-11-03	2460982.90060		4.221		1 x 500		r          r = 19.26 +/- 0.05


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