TITLE: GCN CIRCULAR NUMBER: 34762 SUBJECT: GRB 230812B: r'-band observations from MISTRAL at Observatoire de Haute-Provence DATE: 23/09/24 19:28:39 GMT FROM: Christophe Adami at LAM christophe.adami@lam.fr

P. Amram, C. Adami, S. Basa (LAM/Pythéas), T. Adami (ENS Paris-Saclay), B. Schneider (MIT), A. Saccardi, S. D. Vergani, (GEPI, Obs. de Paris), S. Antier, A. de Ugarte Postigo (OCA), E. Le Floc'h, D. Götz, F. Schüssler, D. Turpin (CEA-Saclay), report, on behalf of a larger collaboration:

We observed the field of GRB 230812B (Fermi GBM Team GCN, 34386 and all subsequent GCNs) using the MISTRAL spectro-imager of Observatoire de Haute Provence (OHP) in imaging mode. We obtained during the 2023 09 22 night 12x600s exposure in the r'-band with a mid-epoch of 20:30 UT.

We derive the following photometry, calibrated against the Pan-STARRS catalog, not corrected for the underlying galaxy, and not corrected for Galactic dust reddening:

2023 09 22 20:30 UT r' = 22.37 +/- 0.14

We acknowledge the excellent support from Yoann Degot-Longhi (Observatoire de Haute Provence) and we thank Isabelle Boisse.

View this GCN Circular online at https://gcn.nasa.gov/circulars/34762. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...