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

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.

15 pages, 2 tables, 5 figures, Accepted in ApJ

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• Timing and spectral studies of Cen X-3 in multiple luminosity states using $\text{AstroSat}$
• Revealing the state transition of Cen X-3 at high spectral resolution with Chandra
• Variations in the X-ray eclipse transitions of Cen X-3
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• Temporal and spectral variations of the X-ray pulsar Cen X-3 observed by NuSTAR
• QPOML: A Machine Learning Approach to Detect and Characterize Quasi-Periodic Oscillations in X-ray Binaries
• Timing and Spectral Analysis of 4U 1626-67 Using AstroSat/LAXPC