C. Adami (LAM), J. Palmerio, S. D. Vergani (GEPI, Obs. de Paris), B. Schneider (MIT), E. Le Floc’h, D. Götz, D.Turpin (CEA Paris-Saclay), S. Basa (LAM) report on behalf of a larger collaboration:
We performed a refined analysis of our spectrum (Adami et al. GCN33741) of GRB 230506C (Tohuvavohu et al., GCN 33731, Jelinek et al. GCN 33735, Moskvitin et al. GCN 33748) taken at OHP/T193 with the MISTRAL spectroscopic blue setting, covering from 4200A to 8000A, at R~750 (midtime = T0+4.4h) .
Despite the very low quality of the spectrum, due to the faintness of the object, we can identify a break that we tentatively interpret as a Lyman-alpha break, and for which we find a corresponding Lyman-limit flux drop, indicating 3.7<z<~4.0.
We acknowledge the excellent support from Observatoire de Haute-Provence, in particular Jean Pierre Troncin, the SOPHIE observer Daniel Sebastian and the LAM AMAZED team.