The detection of polarized x-ray emission from the magnetar 1E 2259+586

TL;DR

This study reports significant polarized X-ray emission from the magnetar 1E 2259+586, revealing insights into its magnetic field and emission mechanisms through multi-instrument observations.

Contribution

It provides the first detailed polarization measurements of this magnetar, supporting a model involving resonant cyclotron scattering in a strong magnetic field.

Findings

Polarization degree exceeds 20% in most phases.

Polarization angle aligns with a rotating vector model.

Surface magnetic field estimated above 10^15 G.

Abstract

We report on IXPE, NICER and XMM-Newton observations of the magnetar 1E 2259+586. We find that the source is significantly polarized at about or above 20% for all phases except for the secondary peak where it is more weakly polarized. The polarization degree is strongest during the primary minimum which is also the phase where an absorption feature has been identified previously (Pizzocaro et al. 2019). The polarization angle of the photons are consistent with a rotating vector model with a mode switch between the primary minimum and the rest of the rotation of the neutron star. We propose a scenario in which the emission at the source is weakly polarized (as in a condensed surface) and, as the radiation passes through a plasma arch, resonant cyclotron scattering off of protons produces the observed polarized radiation. This confirms the magnetar nature of the source with a surface field greater than about 10¹⁵ G