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Quasi-Periodic Pulse Amplitude Modulation in the Accreting Millisecond Pulsar IGR J00291+5934We introduce a new method for analyzing the a periodic variability of coherent pulsations in accreting millisecond X-ray pulsars (AMXPs). Our method involves applying a complex frequency correction to the time-domain lightcurve, 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 a periodic 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.
Document ID
20170010250
Document Type
Reprint (Version printed in journal)
Authors
Bult, Peter
(Universities Space Research Association Greenbelt, MD, United States)
van Doesburgh, Marieke
(Amsterdam Univ. Netherlands)
van der Klis, Michiel
(Amsterdam Univ. Netherlands)
Date Acquired
October 20, 2017
Publication Date
August 18, 2017
Publication Information
ISSN: 2041-8205
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN47541
Funding Number(s)
CONTRACT_GRANT: NNH15CO48B
WBS: WBS 662298
Distribution Limits
Public
Copyright
Other
Keywords
stars
x-ra
binaries
pulsars
neutron
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