1. Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of Accretion-powered Pulsars in the Small Magellanic Cloud with an Unscented Kalman Filter.
- Author
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O'Leary, Joseph, Melatos, Andrew, Kimpson, Tom, O'Neill, Nicholas J., Meyers, Patrick M., Christodoulou, Dimitris M., Bhattacharya, Sayantan, and Laycock, Silas G. T.
- Subjects
SMALL magellanic cloud ,MAGNETIC dipole moments ,X-ray binaries ,STELLAR parallax ,KALMAN filtering - Abstract
Many accretion-powered pulsars rotate in magnetocentrifugal disequilibrium, spinning up or down secularly over multiyear intervals. The magnetic dipole moment μ of such systems cannot be inferred uniquely from the time-averaged aperiodic X-ray flux 〈 L (t)〉 and pulse period 〈 P (t)〉, because the radiative efficiency of the accretion is unknown and degenerate with the mass accretion rate. Here, we circumvent the degeneracy by tracking the fluctuations in the unaveraged time series L (t) and P (t) using an unscented Kalman filter, whereupon μ can be estimated uniquely, up to the uncertainties in the mass, radius, and distance of the star. The analysis is performed on Rossi X-ray Timing Explorer observations for 24 X-ray transients in the Small Magellanic Cloud, which have been monitored regularly for ∼16 yr. As well as independent estimates of μ, the analysis yields time-resolved histories of the mass accretion rate and the Maxwell stress at the disk–magnetosphere boundary for each star, and hence auto- and cross-correlations involving the latter two state variables. The inferred fluctuation statistics convey important information about the complex accretion physics at the disk–magnetosphere boundary. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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