TITLE: GCN CIRCULAR NUMBER: 42077 SUBJECT: GRB 251002A: OHP/T193 MISTRAL optical afterglow detection DATE: 25/10/03 07:34:37 GMT FROM: Christophe Adami at LAM <christophe.adami@lam.fr> N. Mandarakas (LAM), C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), B. Schneider (LAM), E. Le Floc'h (CEA/Irfu), S.D. Vergani (LUX-Paris Obs.) report on behalf of a larger collaboration: We observed the field of the SVOM/ECLARIs GRB 251002 (Saccardi et al., GCN 42060) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained three exposures of 240s (for a total of 12 min) in the r-band starting at 22:05:40 UT on 2025-10-02 (observations mid-time at T-To=2h20min), under modest weather conditions. In the stacked images, we detect the optical counterpart reported and followed by Palmerio et al. (GCN 42061), Turpin et al. (GCN 42062), Jelinek et al. (GCN 42063), Julia-Maroto et al. (GCN 42064), Moskvitin et al. (GCN 42065), Perez-Garcia et al. (GCN 42066), Senik et al. (GCN 42067), Sun et al. (GCN 42075), and Saccardi et al. (GCN 42076) The preliminary magnitude derived for that source is: r’ = 19.39 +/- 0.07 mag (AB) The detection limit (3 sigma) is r=21.10 +/- 0.15 The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025). We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/42077. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...