Timing properties of the X-ray accreting pulsar 1A 0535+262 studied with Insight-HXMT

TL;DR

This study analyzes the timing properties of the X-ray pulsar 1A 0535+262 during a 2020 outburst using Insight-HXMT data, revealing complex pulse profile evolution and a luminosity-dependent dip at the cyclotron resonance energy.

Contribution

First detailed analysis of pulse profile evolution across luminosity regimes for 1A 0535+262 using broadband data from Insight-HXMT.

Findings

Pulse profile varies with energy and luminosity.

A dip at the CRSF energy appears around the critical luminosity.

The dip's luminosity dependence suggests a link to accretion physics.

Abstract

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 sub-critical luminosity to super-critical 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 (CRSFs) 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 $\times 10^{37}$ erg s$^{-1}$ to 1.0 $\times 10^{38}$ erg s$^{-1}$. The observed structure is luminosity dependent and appears around the source critical luminosity ($\sim$ 6.7 $\times 10^{37}$ erg s$^{-1}$).