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..