Pulse profiles of PSR J1023+0038 from January 21, 2023, in the optical (Aqueye+, bottom panel, blue dots) and X-ray (NICER, top panel, green dots) energy bands. Both profiles are fitted with the same model (yellow and red lines; see Eq. 2), folded with the same spin period (see Table 1) and with the same t₀ = 59965.0 MJD. The dashed navy lines in both panels represent the phase of the second harmonic (x₂), used to measure the phase lag, and the light blue shaded bands indicate the corresponding uncertainties.