The magnetar 1E 1547.0-5408: radio spectrum, polarimetry, and timing

TL;DR

This study characterizes the radio emission, polarization, and timing of magnetar 1E 1547.0-5408, revealing unique properties such as high polarization, large rotation measure, and flux variability, distinguishing it from typical pulsars.

Contribution

It provides detailed polarization, spectral, and timing measurements of the magnetar, highlighting its unique radio emission features and their implications for magnetic field and emission geometry.

Findings

Radio flux density is stable across 1.4-45 GHz but varies over time.

Polarization is nearly 100% linear at higher frequencies and becomes depolarized at lower frequencies.

Rotation measure is the largest known for any pulsar, indicating a strong magnetic field along the line of sight.

Abstract

We have investigated the radio emission from the anomalous X-ray pulsar 1E 1547.0-5408 (PSR J1550-5418) using the Parkes telescope and the Australia Telescope Compact Array. The flux density of the pulsar is roughly the same between 1.4 and 45 GHz, but shows time variability. The radiation is nearly 100% linearly polarized between frequencies of 45 and 3.2 GHz, but from 2.3 to 1.4 GHz it becomes increasingly more depolarized. The rotation measure of -1860 rad/m^2 is the largest for any known pulsar, and implies an average magnetic field strength along the line of sight of 2.7 microG. The pulse profiles are circularly polarized at all frequencies observed, more so at lower frequencies, at the ~15% level. The observed swing of the position angle of linear polarization as a function of pulse phase suggests that in this neutron star the rotation and magnetic axes are nearly aligned, and that its radio emission is only detectable within a small solid angle. Timing measurements indicate that the period derivative of this 2 s pulsar has increased by nearly 40% in a 6-month period. The flat spectrum and variability in flux density and pulse profiles are reminiscent of the properties of XTE J1810-197, the only other known radio-emitting magnetar, and are anomalous by comparison with those of ordinary radio pulsars.