TITLE: GCN CIRCULAR NUMBER: 42574 SUBJECT: GRB 251103A: OHP/T193 optical observations DATE: 25/11/04 11:29:23 GMT FROM: Christophe Adami at LAM <christophe.adami@lam.fr> C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), B. Schneider (LAM), S. Basa (UAR Pytheas), E. Le Floc'h (CEA/Irfu) report on behalf of the MISTRAL GRB collaboration: We carried out observations of the GRB 251103A (Hu et al., GCN 42534, Schneider et al., GCN 42535; Fermi GBM Team, GCN 42536; Turpin et al., GCN 42538; Gritsevich et al., GCN 42539, Izzo et al., GCN 42540; Osborne et al., GCN 42551; O'Neill et al., GCN 42543; Ghosh et al., GCN 42545; Schneider et al., GCN 42549; Osborne et al., GCN 42551; Wang et al., GCN 42552; Sonawane et al., GCN 42553; Breeveld et al., GCN 42554; Hellot et al., GCN 42559; Mo et al., GCN 42562; Lipunov et al., GCN 42565; Delaunay et al., GCN 42568; Zheng et al., GCN 42571, Ren et al., GCN 42572) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 94 min (1 exposure of 4 min and 18 exposures of 5 min) in the r-band at a midtime of 2025-11-04 05:24:03 UT corresponding to T-T0 = 24.63 hours. The afterglow is detected in r’ and we measured the following preliminary magnitude: r’ = 22.33 +/- 0.16 The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction. 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/42574. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...