Variations of cyclotron resonant scattering features in Vela X-1 revealed with Insight-HXMT

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 at ~21-27 keV and 43-50 keV for the fundamental and first harmonic, respectively. We present the evolution of spectral parameters and find that two line centroid energy ratio E2/E1 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 CRSF 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.

10 pages, MNRAS in press

References in corpus (13)

• Discovery of a flux-related change of the cyclotron line energy in Her X-1
• A model for cyclotron resonance scattering features
• X-ray Spectral Study of the Photoionized Stellar Wind in Vela~X-1
• Pulse phase resolved analysis of the HMXB Cen X-3 over two binary orbits
• Long-term change in the cyclotron line energy in Hercules X-1
• The clumpy absorber in the high-mass X-ray binary Vela X-1
• Revisiting the archetypical wind accretor Vela X-1 in depth -- A case study of a well-known X-ray binary and the limits of our knowledge
• Short-Term Variability of X-rays from Accreting Neutron Star Vela X-1: I. Suzaku Observations
• The Swift-BAT monitoring reveals a long term decay of the cyclotron line energy in Vela X-1
• Inversion of the decay of the cyclotron line energy in Her X-1
• Relation of cyclotron resonant energy and luminosity in a strongly magnetized neutron star GRO J1008-57 observed by Insight-HXMT
• Probing large-scale wind structures in Vela X-1 using off-states with INTEGRAL
• Timing and spectral variability of high mass X-ray pulsar GX 301--2 over orbital phases observed by Insight-HXMT

Cited by in corpus (5)

• Discovery of Two Cyclotron Resonance Scattering Features in X-ray Pulsar Cen X-3 by Insight-HXMT
• Detection of a quasi-periodic oscillation at $\sim$40 mHz in Cen X-3 with Insight-HXMT
• An in-depth analysis of the variable cyclotron lines in GX 301$-$2
• Temporal and spectral variations of the X-ray pulsar Cen X-3 observed by NuSTAR
• Studying the variations of the cyclotron line in Cen X-3 using Insight-HXMT