TITLE: GCN CIRCULAR NUMBER: 40337 SUBJECT: GRB 250502A: Montarrenti Observatory optical detection DATE: 25/05/03 21:54:31 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 GRB 250502A detected by SVOM/ECLAIRs (Wang et al., GCN 40313) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88).
The observations were started at 2025-05-02 20:42:17 UT (approximately 12 hours after burst) stacking a set of Rc-band CCD images. Observations were performed under thin cloud cover in the second part of the night.
The optical afterglow (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319; Li et al., GCN 40320; Gosh et al., GCN 40322; de Ugarte Postigo et al. with a redshift of z = 2.163, GCN 40328 ; Perez-Fournon et al., GCN 40330; Odeh & Guessoum, GCN 40331; Bochenek & Perley, GCN 40333; Corcoran et al., GCN 40334 and Dichiara et al., GCN 40336) was barely detected (S/N =2.1) at the following position:
RA (J2000.0) 13h 46m 05.60s +/-0.23 Decl. (J2000.0) -10° 45' 31.70" +/-0.16
Preliminary photometry was obtained using nearby PanSTARRS stars as follows:
Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. 2025-05-02 21:31:19 UT 12.75 140x40s Rc 20.70 +/- 0.15
Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied.
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