TITLE: GCN CIRCULAR NUMBER: 35367 SUBJECT: GRB 231215A : OHP/T193 optical afterglow detection DATE: 23/12/15 22:40:38 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com> D. Turpin (CEA Paris-Saclay), C. Adami (LAM), E. Le Floc'h, D. Götz, F. Schüssler (CEA Paris-Saclay), B. Schneider (MIT), S. Basa (Pytheas/OHP/LAM), A. Saccardi, S. D. Vergani (GEPI, Obs. de Paris), report on behalf of a larger collaboration: We observed the field of the long GRB 231215A (D'Avanzo et al., GCN 35343) and its afterglow candidate (Evans et al. GCN 35345) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL instrument. A total of 5 images were taken in r-band (total exposure = 3000s) and 3 others in the g-band (total exposure = 2100s) starting at 17:13:33.32 UT on 2023-12-15, ~7.43h after the trigger. In the combined frames, we clearly detect the optical afterglow reported by Lipunov et al. GCN 35347, Pankov et al. GCN 35349, Sasada et al. GCN 35351, An et al. GCN 35353, Wagh et al. GCN 35354, Hu et al. GCN 35363. The preliminary magnitude derived are the following: ----------------------------------------------- T-T0 (in days, midtime) | mag | filter ----------------------------------------------- 0.3302 | 21.32 ± 0.10 mag (AB) | r' 0.3795 | 21.76 ± 0.07 mag (AB) | g' ----------------------------------------------- The photometric calibration was performed using nearby stars from the PanSTARRS catalog and magnitudes are not corrected for Galactic extinction. Our results are compatibe with the fading behavior observed in previous GCN (Lipunov et al. GCN 35347, Pankov et al. GCN 35349, Sasada et al. GCN 35351, An et al. GCN 35353, Wagh et al. GCN 35354, Ferro et al. GCN 35355, Hu et al. GCN 35363). We note that the afterglow flux decay is steep with a temporal index alpha ~ 1.9. We encourage further follow-up observation with large telescopes to better characterize the flux and spectral evolution of this afterglow. We acknowledge the excellent support from Observatoire de Haute-Provence, in particular Jean Balcaen for the MISTRAL observations and the SOPHIE observer Clément Ranc. View this GCN Circular online at https://gcn.nasa.gov/circulars/35367. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...