Measurements of spin and orbital parameters in Cen X-3 by Insight-HXMT

Abstract

We present a detailed temporal analysis for the eclipsing high-mass X-ray binary system Cen X-3 using the Insight-HXMT data in 2018 and 2020. Three consecutive and high statistic observations among data are used for the precise timing analysis. The pulse profiles are revealed to vary with energy and time. The pulse profiles for the 2018 observations showed a double peak in the low energy bands below 10 keV and evolved to a single peak in higher energies without the correlation between pulse fraction and flux, and profiles in low energies changed with time. But the pulse profile for the 2020 observation only showed a broad single-peaked pulse in all energy bands with a positive relation between pulse fraction and flux, which may indicate the transition of the emission patterns from a mixture of a pencil and a fan beam to a dominated pencil-like beam. With performing a binary orbital fitting of spin periods, we obtain an accurate value for the spin period and the orbital parameters. The intrinsic spin period of the neutron star is found to be $4.79920\pm 0.00006$ s at MJD 58852.697, with the orbital period determined at $P_{\text{orb}}=2.08695634\pm 0.00000001$ day, and its decay rate of -(1.7832 ± 0.0001) × 10⁻⁶ yr⁻¹ for the binary.