Quasi-periodic pulse amplitude modulation in the accreting millisecond pulsar IGR J00291+5934

Abstract

We introduce a new method for analysing the aperiodic variability of coherent pulsations in accreting millisecond X-ray pulsars. Our method involves applying a complex frequency correction to the time-domain light curve, allowing for the aperiodic modulation of the pulse amplitude to be robustly extracted in the frequency domain. We discuss the statistical properties of the resulting modulation spectrum and show how it can be correlated with the non-pulsed emission to determine if the periodic and aperiodic variability are coupled processes. Using this method, we study the 598.88 Hz coherent pulsations of the accreting millisecond X-ray pulsar IGR J00291+5934 as observed with the Rossi X-ray Timing Explorer and XMM-Newton. We demonstrate that our method easily confirms the known coupling between the pulsations and a strong 8 mHz QPO in XMM-Newton observations. Applying our method to the RXTE observations, we further show, for the first time, that the much weaker 20 mHz QPO and its harmonic are also coupled the pulsations. We discuss the implications of this coupling and indicate how it may be used to extract new information on the underlying accretion process.

12 pages, 7 figures, 1 table. Accepted for publication in ApJ

References in corpus (13)

• A quasi-periodic modulation of the iron line centroid energy in the black hole binary H 1743-322
• Phase-resolved spectroscopy of low frequency quasi-periodic oscillations in GRS 1915+105
• A Double Outburst from IGR J00291+5934: Implications for Accretion Disk Instability Theory
• Millihertz Oscillation Frequency Drift Predicts the Occurrence of Type I X-ray Bursts
• Reaction Rate and Composition Dependence of the Stability of Thermonuclear Burning on Accreting Neutron Stars
• Observations of the 599 Hz Accreting X-ray Pulsar IGR J00291+5934 during the 2004 Outburst and in Quiescence
• Spectral and timing properties of IGR J00291+5934 during its 2015 outburst
• The 2015 outburst of the accretion-powered pulsar IGR J00291+5934: INTEGRAL and Swift observations
• Discovery of the INTEGRAL X/Gamma-ray transient IGR J00291+5934: a Comptonised accreting ms pulsar ?
• Testing the relativistic precession model using low frequency and kHz quasi-periodic oscillations in neutron star low mass X-ray binaries with known spin
• Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934
• The stochastic X-ray variability of the accreting millisecond pulsar MAXI J0911-655
• Discovery of 1-5 Hz flaring at high luminosity in SAX J1808.4-3658

Cited by in corpus (2)

• Long-term coherent timing of the accreting millisecond pulsar IGR J17062-6143
• The stochastic X-ray variability of the accreting millisecond pulsar IGR J17062-6143