Tracking hidden magnetospheric fluctuations in accretion-powered pulsars with a Kalman filter

TL;DR

This paper introduces a Kalman filter approach to analyze flux and pulse period data from accretion-powered pulsars, revealing hidden magnetospheric fluctuations and providing insights into disk-magnetosphere interactions.

Contribution

It presents a novel application of Kalman filtering to estimate unobservable variables in pulsar accretion physics, enhancing understanding of magnetospheric dynamics.

Findings

Estimated stochastic fluctuations of mass accretion rate, Maxwell stress, and radiative efficiency.

Implications for hydromagnetic instabilities at the disk-magnetosphere boundary.

Potential for improved gravitational wave searches from X-ray binaries.

Abstract

X-ray flux and pulse period fluctuations in an accretion-powered pulsar convey important information about the disk-magnetosphere interaction. It is shown that simultaneous flux and period measurements can be analysed with a Kalman filter based on the standard magnetocentrifugal accretion torque to generate accurate time-dependent estimates of three hidden state variables, which fluctuate stochastically and cannot be measured directly: the mass accretion rate, the Maxwell stress at the disk-magnetosphere boundary, and the radiative efficiency of accretion onto the stellar surface. The inferred fluctuation statistics carry implications for the physics of hydromagnetic instabilities at the disk-magnetosphere boundary and searches for continuous gravitational radiation from low-mass X-ray binaries.