Phase dependent evolution within large luminosity range of 1A 0535+262 observed by Insight-HXMT during 2020 giant outburst

• Published in: arXiv.org 2022-04
• Main Authors: Ling-Da Kong, Zhang, Shu, Long, Ji, Doroshenko, Victor, Santangelo, Andrea, Orlandini, Mauro, Frontera, Filippo, Li, Jian, Yu-Peng, Chen, Peng-Ju, Wang, Chang, Zhi, Jin-Lu, Qu, Zhang, Shuang-Nan
• Format: Article
• Language: English
• Subjects: Cyclotron resonance; Deposition; Energy bands; Luminosity; Pulsars; Resonance scattering; Spectrum analysis
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2204.11222

We have performed phase-resolved spectral analysis of the accreting pulsar 1A~0535+262 based on observations of Insight-HXMT during the 2020 Type-II outburst of the source. We focus on the two-dimensional dependence of the cyclotron resonance scattering features (CRSFs) along the outburst time and at different phases. The fundamental CRSF line (f-CRSF) shows different time- and phase-dependent behaviors. At higher luminosity, the phase profile of the f-CRSF energy changes from a single peak to double peaks, with the transition occurring at MJD 59185. On the contrary, the first harmonic CRSF (1-st CRSF) at \(\sim\) 100 keV is only detected within a narrow phase range (0.8\(-\)1.0) accompanied by a shallow f-CRSF line. 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.