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arXiv · 2106.14603

Timing and spectral variability of high mass X-ray pulsar GX 301--2 over orbital phases observed by Insight-HXMT

Y. Z. Ding·W. Wang·P. R. Epili·Q. Liu·M. Y. Ge·F. J. Lu·J. L. Qu·L. M. Song·S. Zhang·S. N. Zhang
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Abstract

We report the orbital X-ray variability of high mass X-ray binary (HMXB) GX301--2. GX301--2 undergone a spin up process in 2018--2020 with the period evolving from $\sim$ 685 s to 670 s. The energy resolved pulse-profiles of the pulsar in 1--60 keV varied from single peaked and sinusoidal shapes to multi-peaked across different orbital phases. Pulse fractions evolving over orbit had negative correlations with the X-ray flux. The broad-band X-ray energy spectrum of the pulsar can be described with a partial covering negative positive cutoff power-law continuum model. Near the periastron passage of the pulsar we found a strong variation in the additional column density ($NH_{2}$), which correlated with variation of the flux. Curves of growth for both Fe K$\alpha$ and Fe K$\beta$ lines were plotted to investigate the distribution of matter around neutron star. We have also found the evidence of two cyclotron absorption lines in the phase-averaged spectra in GX301--2, with one line of 30--42 keV and the other line varying in 48--56 keV. Both two line's centroid energies show the similar relationship with X-ray luminosity: positive correlation in lower luminosity range, and negative relation above a critical luminosity of $10^{37}$ erg s$^{-1}$. We estimated the surface magnetic field of the neutron star in GX301--2 at ~$(0.5-2)\times 10^{13}$ G. Two cyclotron line energies have a nearly fixed ratio of ~1.63 while having a low strength ratio (~0.05), suggesting that these two features may actually be one line.

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Y. Z. Ding, W. Wang, P. R. Epili, Q. Liu, M. Y. Ge, F. J. Lu, J. L. Qu, L. M. Song, S. Zhang, S. N. Zhang. 2021-06-28. Timing and spectral variability of high mass X-ray pulsar GX 301--2 over orbital phases observed by Insight-HXMT. https://doi.org/10.1093/mnras%2Fstab1862

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