TITLE: GCN CIRCULAR NUMBER: 39777 SUBJECT: GRB 250317B: OHP/T193 continued follow-up DATE: 25/03/19 08:16:18 GMT FROM: Emeric Le Floc'h at CEA-Saclay emeric.lefloch@cea.fr
B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Ugarte Postigo (LAM), M. Dennefeld (IAP/CNRS/Sorbonne U.) and D. Turpin (CEA/Irfu) report on behalf of the MISTRAL-GRB collaboration:
We performed additional observations of the optical counterpart of GRB 250317B (Zhao et al., GCN 39753; Watson et al., GCN 39754; Palmerio et al., GCN 39755; Pérez-Fournon et al., GCN 39757; Ghosh et al., GCN 39759, Ferro et al., GCN 39764, Schneider et al., GCN 39767; Thöne et al., GCN 39769; Zhu et al., GCN 39770; Pankov et al., GCN 39772; Moretti et al., GCN 39774) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 1 exposure of 600s and 5 exposures of 720s in the r-band starting at 19:22 UT on 2025-03-18 (1.84 days after the trigger). In the final stacked image, the afterglow is marginally detected, at a level much fainter than the phase of rebrightening reported earlier by Thöne et al. (GCN 39769) and Zhu et al. (GCN 39770).
The preliminary magnitude derived for the source is :
r = 23.5 +/- 0.4 mag (AB)
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction.
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen et Andres Carmona for the MISTRAL observations.
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