The Magnetic Field of the Solar Corona from Pulsar Observations

TL;DR

This paper introduces a new method using pulsar observations to independently measure the solar corona's magnetic field and electron density, providing direct insights without relying on assumptions about the plasma distribution.

Contribution

The study demonstrates a novel observational technique combining Faraday rotation and dispersion measurements to directly determine the magnetic field in the solar corona.

Findings

Detected increased Faraday rotation at 0.95° from the Sun's center.

Estimated a lower limit of 393 μG for the magnetic field strength.

Constrained the magnetic field to about 20 mG at 2.5 solar radii using models.

Abstract

We present a novel experiment with the capacity to independently measure both the electron density and the magnetic field of the solar corona. We achieve this through measurement of the excess Faraday rotation due to propagation of the polarised emission from a number of pulsars through the magnetic field of the solar corona. This method yields independent measures of the integrated electron density, via dispersion of the pulsed signal and the magnetic field, via the amount of Faraday rotation. In principle this allows the determination of the integrated magnetic field through the solar corona along many lines of sight without any assumptions regarding the electron density distribution. We present a detection of an increase in the rotation measure of the pulsar J1801$-$2304 of approximately 160 \rad at an elongation of 0.95$^\circ$ from the centre of the solar disk. This corresponds to a lower limit of the magnetic field strength along this line of sight of $> 393\mu\mathrm{G}$. The lack of precision in the integrated electron density measurement restricts this result to a limit, but application of coronal plasma models can further constrain this to approximately 20mG, along a path passing 2.5 solar radii from the solar limb. Which is consistent with predictions obtained using extensions to the Source Surface models published by Wilcox Solar Observatory