TITLE: GCN CIRCULAR NUMBER: 35286 SUBJECT: GRB 231205B: r'-band observations from MISTRAL at Observatoire de Haute-Provence DATE: 23/12/06 09:41:50 GMT FROM: Christophe Adami at LAM <christophe.adami@lam.fr> C. Adami (LAM), E. Le Floc'h, D. Götz, F. Schüssler,D. Turpin (CEA Paris-Saclay), A. de Ugarte Postigo (OCA/CNRS), S. Basa (LAM), S. D. Vergani (GEPI, Obs. de Paris), report on behalf of a larger collaboration: We observed the field of GRB231205B (GCN 35269; Evans et al., GCN 35270, Odeh et al.) using the MISTRAL spectro-imager mounted at the T193cm telescope at Observatoire de Haute-Provence (France) under a poor seeing of ~3arcsec. We began our observations on 2023 05 December 20:56:18 UT (~5.2h after the trigger time) with a series of r'-band (300s + 6x720s) images. Last image was taken at 22:26:25 UT. Consistently with Evans et al. and Odeh et al., we do not detect any credible optical counterpart to GRB231205B within the GCN 35269 Swift XRT error box. Using the r-band PanStarr public image, the faintest detected object in our r-band image with a measured PanStarr magnitude is at rmeanKronmag=20.65. Using the i-band PanStarr public image, the faintest detected object in our r-band image with a measured PanStarr magnitude is at imeanKronmag=21.60. We acknowledge the excellent support from Observatoire de Haute-Provence, in particular Jean Balcaen.. View this GCN Circular online at https://gcn.nasa.gov/circulars/35286. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...