2022ApJ...935..125W

We report results on the timing analysis of the 2020 giant outburst of 1A 0535+262, using broadband data from Insight-HXMT. The analysis of the pulse profile evolution from the subcritical-luminosity to the supercritical-luminosity regime is presented for the first time. We found that the observed pulse profile exhibits a complex dependence on both energy and luminosity. A dip structure at the energy of the cyclotron resonant scattering features is found for the first time in the pulse fraction-energy relation of 1A 0535+262, when the outburst evolves in a luminosity range from 4.8 × 10³⁷ to 1.0 × 10³⁸ erg s^–1. The observed structure is luminosity dependent and appears around the source critical luminosity (∼6.7 × 10³⁷ erg s^–1).