Phase dependent evolution within large luminosity range of 1A 0535+262 observed by Insight-HXMT during 2020 giant outburst
In 2020 1A~0535+262 surprised us with a quite spectacular outburst, which allowed to exploit Insight-HXMTto it's fullest and part of the results appear now in our paper led by collegues from IHEP. We focus on the two-dimensional dependence of the cyclotron resonance scattering features (CRSFs) along the outburst time and at different phases. The basic result seen also in figure below is that CRSF fundamental shows different time- and phase-dependent behaviors compared to harmonic. Based on these results, we speculate that when the source enters the supercritical regime, the higher accretion column can significantly enhance the harmonic line at a narrow phase through an "anti-pencil" beam at a higher energy band. At the same time, it will also affect the behavior of the fundamental line.