Detection of a quasi-periodic oscillation at $\sim$40 mHz in Cen X-3 with Insight-HXMT

Abstract

We investigated the quasi-periodic oscillation (QPO) features in the accretion-powered X-ray pulsar Cen X-3 observed by Insight-HXMT. For two observations in 2020 when Cen X-3 was in an extremely soft state, the power density spectrum revealed the presence of obvious QPO features at $\sim$40 mHz with an averaged fractional rms amplitude of $\sim 9\%$. We study the mHz QPO frequency and rms amplitude over orbital phases, and find that the QPO frequency is $\sim$33-39 mHz at the orbital phase of 0.1-0.4, increasing to $\sim$37-43 mHz in the orbital phase of 0.4-0.8, but has no strong dependence on X-ray intensity. We also carried out an energy-dependent QPO analysis, the rms amplitude of the mHz QPOs have a decreasing trend as the energy increases from 2 to 20 keV. In addition, the QPO time-lag analysis shows that the time delay is $\sim 20$ ms (a hard lag) in the range of $\sim$5-10 keV, and becomes negative (time lag of $-(20-70)$ ms) above $\sim 10$ keV. The different QPO theoretical models are summarized and discussed. In the end, we suggest that these energy-dependent timing features as well as the origin of mHz QPOs in Cen X-3 may be ascribed to an instability when the accretion disk is truncated near the corotation radius.

9 pages, MNRAS in press

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Cited by in corpus (4)

• X-Ray Views of Galactic Accreting Pulsars in High-Mass X-Ray Binaries
• Sidebands to mHz QPOs in 4U 1626$-$67 in the second spin-down state
• Temporal and spectral variations of the X-ray pulsar Cen X-3 observed by NuSTAR
• Studying the variations of the cyclotron line in Cen X-3 using Insight-HXMT