Radio properties of the magnetar near Sagittarius A* from observations with the Australia Telescope Compact Array

TL;DR

This study reports detailed radio observations of a magnetar near Sagittarius A*, revealing its high dispersion and rotation measures, strong linear polarization, and variable flux density, contributing valuable data on magnetar radio properties in the galactic center.

Contribution

First detailed radio measurements of a magnetar near Sagittarius A* across multiple frequencies, highlighting its extreme dispersion and rotation measures and polarization characteristics.

Findings

Highest dispersion measure among known pulsars

Largest rotation measure ever measured for a pulsar

Flux density increased by a factor of two over 30 days

Abstract

We have carried out observations of the newly-discovered magnetar in the direction of Sagittarius A* using the Australia Telescope Compact Array in four frequency bands from 4.5 to 20 GHz. Radio pulsations are clearly detected at all frequencies. We measure the pulsar's dispersion measure to be 1650 +/- 50 pc/cm^3, the highest of any of the known pulsars. Once Faraday rotation has been taken into account, the pulse profile is more than 80% linearly polarized at all frequencies and has a small degree (5%) of circular polarization. The rotation measure of -67000 +/- 500$ rad/m^2 is the largest (in magnitude) ever measured for a pulsar but still a factor 8 smaller than Sgr A* itself. The combination of the dispersion and rotation measures implies an integrated magnetic field strength of -50uG along the line of sight. The flux density appears to have increased by about a factor of two between observations made 30 days apart. This object therefore joins the small class of radio emitting magnetars.