Quasi-periodic Pulse Amplitude Modulation in the Accreting Millisecond Pulsar IGR J00291+5934

We introduce a new method for analyzing the aperiodic variability of coherent pulsations in accreting millisecond X-ray pulsars (AMXPs). 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 robu...

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Bibliographic Details
Published in:The Astrophysical journal 2017-08, Vol.845 (2), p.124
Main Authors: Bult, Peter, Doesburgh, Marieke van, Klis, Michiel van der
Format: Article
Language:English
Subjects:
AMPLITUDES
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
CORRECTIONS
COSMIC X-RAY BURSTS
Coupling
Deposition
EMISSION
HARMONICS
Light curve
MHZ RANGE
Millisecond pulsars
MODULATION
PERIODICITY
PULSARS
pulsars: general
PULSATIONS
Pulse amplitude modulation
Quasi-Periodic Oscillations
SPECTRA
STARS
stars: neutron
VISIBLE RADIATION
X-rays: binaries
X-rays: individual (IGR J00291+5934)
XMM (spacecraft)
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Summary:We introduce a new method for analyzing the aperiodic variability of coherent pulsations in accreting millisecond X-ray pulsars (AMXPs). 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 AMXP 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 quasi-periodic oscillation (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 with 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.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aa8172