Studying the variations of the cyclotron line in Cen X-3 using Insight-HXMT

TL;DR

This study analyzes the cyclotron resonant scattering features of Cen X-3 using Insight-HXMT data, detecting a 29 keV line and exploring its phase-dependent behavior, revealing no correlation with luminosity or time.

Contribution

It provides the first detection of the 29 keV CRSF in Cen X-3 with Insight-HXMT and examines its phase-dependent variation, offering new insights into the pulsar's magnetic field structure.

Findings

Detected the 29 keV cyclotron line in Cen X-3.

Found no correlation between CRSF energy and luminosity or time.

Observed phase-dependent variation of the CRSF centroid energy.

Abstract

We investigate the cyclotron resonant scattering features (CRSFs) of the accreting X-ray pulsar Cen X-3 and significantly detect the 29 keV cyclotron line features in the hard X-ray averaged spectroscopy studies based on the recent Insight-HXMT observations in 2022, when Cen X-3 has X-ray luminosity $L_{\rm X} > \sim 5 \times 10^{37}$ erg\ s$^{-1}$ in the bands of 2 -- 60 keV. We do not find a harmonic line in the average spectra based on different continuum models. We showed that the CRSF energies have no correlation with time or luminosity in the average spectra. In addition, by performing a pulse phase-dependent spectral analysis, we revealed the fundamental line with the centroid energy ranging from 25 to 29 keV with a high significance over the spin phases. The evolution of the cyclotron line centroid energies over pulse phase is similar to the shape of pulse profiles, illustrating a positive correlation between the energy of CRSFs and the pulse phase flux.