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arXiv · 2206.00179

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

Q. Liu·W. Wang·X. Chen·Y. Z. Ding·F. J. Lu·L. M. Song·J. L. Qu·S. Zhang·S. N. Zhang
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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.

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Q. Liu, W. Wang, X. Chen, Y. Z. Ding, F. J. Lu, L. M. Song, J. L. Qu, S. Zhang, S. N. Zhang. 2022-06-01. Variations of cyclotron resonant scattering features in Vela X-1 revealed with Insight-HXMT. https://doi.org/10.1093/mnras%2Fstac1520

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