Orbital- and Spin-phase Variability in the X-Ray Emission from the Accreting Pulsar Centaurus X-3

We present a time-resolved analysis using 39 ks NuSTAR observation data of the X-ray pulsar Centaurus X-3, covering an orbital-phase interval of phi = 0.199-0.414. The orbital- and spin-phase variabilities are investigated through time-resolved spectra, light curves, and pulse profiles. The orbital-phase variability was due to the mixture of two comparable effects: intrinsic flux variability of similar to 10% and obscuration by the clumpy stellar wind. The typical size and number density of the clumps are similar to 9 x 10(10) cm and similar to 3 x 10(12) cm(-3), respectively. In the spin-phase-resolved analysis, we detected variations in the spectral features of the continuum, the Fe line, and the cyclotron resonance scattering feature (CRSF). The photon index ranged from 0.72 to 1.06, corresponding to the difference in the Comptonization optical depth by a factor of similar to 1.6. The equivalent width and intensity of the Fe line had negative correlations with the continuum flux. The central energy and the strength of the CRSF increased at the pulse maximum. The former ranged from 26.0 to 28.7 keV, while the latter varied by a factor of similar to 1.9. The pulse profile was double-peaked in the low-energy band, and it gradually shifted to being single-peaked with energy, indicating the existence of two distinct emission patterns, corresponding to the pencil and fan beams. Finally, we found that the pulse profiles were highly stable along the orbital phase, within a variation degree of similar to 20%, which provides evidence of the highly stable accretion stream of the binary system.

Automated summary

We conducted time-resolved analysis on the X-ray pulsar Centaurus X-3 using 39 ks NuSTAR observation data, focusing on the orbital-phase interval of phi = 0.199-0.414. The study investigated the variability in both orbital and spin phases through analysis of time-resolved spectra, light curves, and pulse profiles. The results showed that the orbital-phase variability was caused by a combination of intrinsic flux variability and obscuration by the clumpy stellar wind, while the spin-phase analysis revealed variations in spectral features such as the continuum, Fe line, and CRSF.