Properties of the stellar surface regions occulted by GJ 436b in ESPRESSO Visits 1 (blue) and 2 (red), derived from the fits to individual exposures. Vertical bars indicate their associated 1σ highest density intervals. Horizontal bars indicate the duration of each exposure. Solid lines are derived from the best RM Revolutions fit to the CCF_intr maps (contrast and FWHM are specific to each visit and colored accordingly). The dotted line in the top panel is the best Reloaded RM fit to the surface RV series, nearly identical to the model from the RM Revolutions fit. Dashed vertical lines are the transit contacts.