Journal article
Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of Accretion-powered Pulsars in the Small Magellanic Cloud with an Unscented Kalman Filter
J O’Leary, A Melatos, T Kimpson, NJ O’Neill, PM Meyers, DM Christodoulou, S Bhattacharya, SGT Laycock
Astrophysical Journal | IOP Publishing Ltd | Published : 2024
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 obse..
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Grants
Awarded by Australian Research Council
Funding Acknowledgements
The authors thank Filippo Anzuini, Julian Carlin, Nathalie Deganaar, Konstantinos Kovlakas, Alessandro Patruno, Phil Uttley, Andres Vargas, and Rudy Wijnands for helpful discussions about Bayesian inference, X-ray timing data, and high-energy astrophysics. We also acknowledge a helpful discussion with Robin Evans regarding unscented Kalman filters. This research was supported by the Australian Research Council Centre of Excellence for Gravitational Wave Discovery, grant No. CE170100004. N.J.O.N. is the recipient of a Melbourne Research Scholarship. D.M.C. acknowledges funding through the National Science Foundation Astronomy and astrophysics research grant No. 2109004. D.M.C., S.B., and S.G.T.L. acknowledge funding through the National Aeronautics and Space Administration Astrophysics Data Analysis Program grant No. NNX14-AF77G.