Quasiperiodic oscillations in Cen X-3 and the long term intensity variations

TL;DR

This study analyzes quasi-periodic oscillations (QPOs) in the X-ray pulsar Cen X-3 over four years, revealing frequency clustering and independence from X-ray intensity, challenging existing models of QPO generation.

Contribution

It provides the first detailed long-term analysis of QPO properties in Cen X-3, showing frequency clustering and independence from X-ray intensity, suggesting alternative QPO mechanisms.

Findings

QPOs detected in 11 out of 81 observations.

QPO frequencies cluster around 40 and 90 mHz.

QPO rms variation is energy independent.

Abstract

We have investigated properties of the Quasi Periodic Oscillation (QPO) features in the accretion powered X-ray pulsar Cen X-3 over a period of about four years using observations carried out with the Proportional Counter Array (PCA) of the {\it {Rossi X-ray Timing Explorer}}. The observations cover a wide range of X-ray intensity of the source in excess of the binary intensity modulation. We have detected QPOs in 11 out of a total 81 pointings with the PCA with rms intensity fluctuation upto 10%. The QPO peak frequency shows clustering around 40 and 90 mHz with the QPO frequency having no dependence on X-ray intensity. This indicates that either (a) the observed X-ray luminosity of the source is not related to the mass accretion rate or inner radius of the accretion disk or (b) that the QPO generation mechanism in Cen X-3 is different from the beat frequency model or Keplerian frequency model that is believed to be operational in most other transient and persistent X-ray pulsars. We have also found that, the rms variation in the 40 mHz QPO feature is not dependent on the X-ray energy, indicating that disk absorption related origin for the QPO is unlikely.