Pulse profiles obtained by folding with 16 phase bins of simultaneous observations with NICER (blue points, left y-axis scale) and Aqueye+ (red points, right y-axis scale) in February 2019 (top panel), January 2020 (middle panel), and January 2022 (bottom panel). Solid lines indicate the best-fitting two-harmonic functions. The zero of the pulse phase was shifted arbitrarily in each panel by the same amount for both instruments.