# Testing the accuracy of the ionospheric Faraday rotation corrections through LOFAR observations of bright northern pulsars

## TL;DR

This study evaluates the accuracy of ionospheric Faraday rotation corrections using LOFAR pulsar observations, demonstrating that with optimal models, corrections can reach an accuracy of approximately 0.06–0.07 rad m$^{-2}$ over a year.

## Contribution

It assesses the performance of different ionospheric models in correcting Faraday rotation in pulsar data, highlighting the potential for high-precision measurements.

## Key findings

- Optimal ionospheric maps achieve correction accuracy of ~0.06–0.07 rad m$^{-2}$ over one year.
- Residual unmodelled effects introduce systematics and correlated noise.
- Comparison of free-electron density maps informs best practices for ionospheric correction.

## Abstract

Faraday rotation of polarized emission from pulsars measured at radio frequencies provides a powerful tool to investigate the interstellar and interplanetary magnetic fields. However, besides being sensitive to the astrophysical media, pulsar observations in radio are affected by the highly time-variable ionosphere. In this article, the amount of ionospheric Faraday rotation has been computed by assuming a thin layer model. For this aim, ionospheric maps of the free electron density (based on Global Positioning System data) and semi-empirical geomagnetic models are needed. Through the data of five highly polarized pulsars observed with the individual German LOw-Frequency ARray stations, we investigate the performances of the ionospheric modelling. In addition, we estimate the parameters of the systematics and the correlated noise generated by the residual unmodelled ionospheric effects, and show the comparison of the different free-electron density maps. For the best ionospheric maps, we have found that the rotation measure corrections on one-year timescales after subtraction of diurnal periodicity are accurate to $\sim$ 0.06--0.07 rad m$^{-2}$.