TITLE: GCN CIRCULAR NUMBER: 38811 SUBJECT: GRB 250103A: Montarrenti Observatory optical detection DATE: 25/01/04 02:03:31 GMT FROM: Simone Leonini at Montarrenti Observatory (Siena, Italy) s.leonini@iol.it
S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report:
We observed the field of SVOM triggered GRB 250103A (Wang et al., GCN 38786, GCN 38787) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88).
The observations were started at 2025-01-03 17:58:28 UT (approximately 8 hours after burst) stacking a set of Ic-band CCD images. Observations were performed under thin cloud cover in the first part of the night.
The OT was barely detected (S/N =1.7) at the following position:
RA (J2000.0) 01h 28m 15.28s +/-0.05 Decl. (J2000.0) -05° 03' 06.59" +/-0.12
Preliminary photometry was obtained using nearby PanSTARRS stars as follows:
Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. UL (3-sigma) 2025-01-03 18:55:32 UT 8.98 111x40s Ic 20.7 S/N =1.7 >20.4
Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied.
Our observations are consistent with other already reported (Li et al., GCN 38795; Qiu et al., GCN 38802; Xu et al., GCN 38808).
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