The NANOGrav 12.5-Year Data Set: Polarimetry and Faraday Rotation Measures from Observations of Millisecond Pulsars with the Green Bank Telescope

TL;DR

This paper presents polarization profiles and Faraday rotation measures for 23 millisecond pulsars, providing insights into pulsar emission geometry and the Galactic magnetic field, with new polarization data for nine pulsars and detection of magnetic field variations.

Contribution

It introduces new polarization profiles for nine pulsars, measures Faraday rotation for 23 pulsars, and analyzes Galactic magnetic field variations using 12.5 years of data.

Findings

First published radio polarization profiles for nine pulsars.

Detection of very low intensity profile components in four pulsars.

Identification of both periodic and stochastic variations in Galactic magnetic field.

Abstract

In this work, we present polarization profiles for 23 millisecond pulsars observed at 820 MHz and 1500 MHz with the Green Bank Telescope as part of the NANOGrav pulsar timing array. We calibrate the data using Mueller matrix solutions calculated from observations of PSRs B1929+10 and J1022+1001. We discuss the polarization profiles, which can be used to constrain pulsar emission geometry, and present both the first published radio polarization profiles for nine pulsars and the discovery of very low intensity average profile components ("microcomponents") in four pulsars. Using the Faraday rotation measures, we measure for each pulsar and use it to calculate the Galactic magnetic field parallel to the line of sight for different lines of sight through the interstellar medium. We fit for linear and sinusoidal trends in time in the dispersion measure and Galactic magnetic field and detect magnetic field variations with a period of one year in some pulsars, but overall find that the variations in these parameters are more consistent with a stochastic origin.