TITLE: GCN CIRCULAR NUMBER: 40275 SUBJECT: EP250427a / GRB 250427A: OHP/T193 photometric observations DATE: 25/04/29 08:49:00 GMT FROM: Christophe Adami at LAM christophe.adami@lam.fr
P. Amram (LAM/AMU), C. Adami (LAM/Pytheas/AMU), S. Vergani (CNRS, Obs. de Paris, LUX), S. Basa (Pytheas/OHP/LAM), A. Saccardi (CEA/Irfu), B. Schneider (LAM) report on behalf of the MISTRAL-GRB collaboration:
We observed EP250427a / GRB 250427A (Wang et al. GCN 40257, Ravasio et al. GCN 40262) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager in blue setting.
We obtained 2x60sec + 120sec + 3x600sec in the r’ band starting at 02:55:47UT on 2025-04-28 (T0+23.3 h after the trigger). The optical afterglow reported by Perez-Garcia et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Chornock et al. GCN 40265; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272; Busmann et al. GCN 40273 is detected at a preliminar value of r = 20.3 +/- 0.15 mag (AB).
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction.
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen and Yoann Degot-Longhi.
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