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

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 ($N{H}_2$), 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.

14 pages, 14 figures and 1 table in the main content, and 1 table and 1 figure in the appendix, accept for publication in MNRAS

References in corpus (9)

• The critical accretion luminosity for magnetized neutron stars
• VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301-2
• An XMM-Newton view of FeKα in HMXBs
• Stellar Wind Accretion in GX301-2: Evidence for a High-density Stream
• Observations of a GX 301-2 Apastron Flare with the X-Calibur Hard X-Ray Polarimeter Supported by NICER, the Swift XRT and BAT, and Fermi GBM
• Orbital phase resolved spectroscopy of GX 301-2 with MAXI
• Discovery of a retrogradely rotating neutron star in the X-ray pulsar GX 301$-$2
• X-ray reprocessing in accreting pulsar GX 301-2 observed with Insight-HXMT
• The spatial distribution of circumstellar material of the wind-fed system GX 301-2

Cited by in corpus (6)

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• Variations of cyclotron resonant scattering features in Vela X-1 revealed with Insight-HXMT
• A NuSTAR observation of the eclipsing binary system OAO 1657-415: The revival of the cyclotron line
• An in-depth analysis of the variable cyclotron lines in GX 301$-$2
• Evolution of eccentric high-mass X-ray binaries. The case of GX 301-2
• Studying the variations of the cyclotron line in Cen X-3 using Insight-HXMT