Radio polarimetry of Galactic centre pulsars

TL;DR

This study measures Faraday rotation of pulsars near the Galactic center to infer magnetic field strength and structure, revealing large-scale magnetic fields and the potential for discovering more pulsars in this region.

Contribution

It provides new measurements of rotation measures for GC pulsars, indicating the magnetic field orientation and strength, and highlights the complexity of electron density models in the GC.

Findings

Large RMs indicate strong magnetic fields (~16-33 microgauss).

Existence of low-scattering corridors suggests more pulsars can be detected.

The electron density model oversimplifies GC structure.

Abstract

To study the strength and structure of the magnetic field in the Galactic centre (GC) we measured Faraday rotation of the radio emission of pulsars which are seen towards the GC. Three of these pulsars have the largest rotation measures (RMs) observed in any Galactic object with the exception of Sgr A*. Their large dispersion measures, RMs and the large RM variation between these pulsars and other known objects in the GC implies that the pulsars lie in the GC and are not merely seen in projection towards the GC. The large RMs of these pulsars indicate large line-of-sight magnetic field components between ~ 16-33 microgauss; combined with recent model predictions for the strength of the magnetic field in the GC this implies that the large-scale magnetic field has a very small inclination angle with respect to the plane of the sky (~ 12 degrees). Foreground objects like the Radio Arc or possibly an ablated, ionized halo around the molecular cloud G0.11-0.11 could contribute to the large RMs of two of the pulsars. If these pulsars lie behind the Radio Arc or G0.11-0.11 then this proves that low-scattering corridors with lengths >~ 100 pc must exist in the GC. This also suggests that future, sensitive observations will be able to detect additional pulsars in the GC. Finally, we show that the GC component in our most accurate electron density model oversimplifies structure in the GC.