Spectrum of GRB230506C taken by MISTRAL (30 min exposure). The thin black curve represents the full spectrum, and the thick black curve represents the spectrum rebinned by 20 pixels. The gray shaded area represents the error spectrum. The center of the expected Ly α positions for z = 3.7 and z = 4 is shown as the vertical blue line. The blue shaded area represents the possible values of the Ly α centroid, assuming that the drop at 6100 A is due to the Lyman break.