Variations of cyclotron resonant scattering features in Vela X-1 revealed with Insight-HXMT. Issue 2 (2nd June 2022)

• Record Type: Journal Article
• Authors: Liu, Q; Wang, W; Chen, X; Ding, Y Z; Lu, F J; Song, L M; Qu, J L; Zhang, S; Zhang, S N
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 514:Issue 2(2022)
• Page Start: 2805
• Page End: 2814
• Publication Date: 2022-06-02
• Subjects: stars: magnetic field -- stars: neutron -- pulsars: individual: Vela X-1 -- X-rays: binaries; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac1520
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present a detailed study of the high-mass X-ray binary Vela X-1, using observations performed by Insight-HXMT in 2019 and 2020, concentrating on timing analysis and spectral studies including pulse phase-resolved spectroscopy. The cyclotron line energy is found to be ∼21–27 and 43–50 keV for the fundamental and first harmonic, respectively. We present the evolution of spectral parameters and find that the two line centroid energy ratio E 2 / E 1 evolved from ∼2 before MJD 58900 to ∼1.7 after that. The harmonic cyclotron line energy has no relation to the luminosity but the fundamental line energy shows a positive correlation with X-ray luminosity, suggesting that Vela X-1 is located in the sub-critical accreting regime. In addition, the pulse phase-resolved spectroscopy in Vela X-1 is performed. Both the cyclotron resonant scattering feature and continuum parameters show strong variability over the pulse phase with the ratio of two line energies about 2 near the peak phases and down to ∼1.6 around off-peak phases. Long-term significant variations of the absorption column density and its evolution over the pulse phase may imply the existence of the clumpy wind structure near the neutron star.