Polarized x-rays from a magnetar

TL;DR

This paper reports the first detection of linearly polarized X-ray emission from a magnetar, revealing energy-dependent polarization that supports the existence of vacuum birefringence in ultra-magnetized neutron stars.

Contribution

It presents the first measurement of polarized X-ray emission from a magnetar, providing new insights into neutron star surface and magnetosphere properties and quantum vacuum effects.

Findings

Detected 12% polarization degree in 2-8 keV band

Observed polarization variation with energy, up to 41% at higher energies

Supported the presence of vacuum birefringence effects

Abstract

We report on the first detection of linearly polarized x-ray emission from an ultra-magnetized neutron star with the Imaging X-ray Polarimetry Explorer (IXPE). The IXPE 35 observations of the anomalous x-ray pulsar 4U 0142+61 reveal a linear polarization degree of $(12\pm 1)\%$ throughout the IXPE 2--8 keV band. We detect a substantial variation of the polarization with energy: the degree is $(14\pm 1)\%$ at 2--4 keV and $(41\pm 7)\%$ at 5.5--8 keV, while it drops below the instrumental sensitivity around 4--5 keV, where the polarization angle swings by $\sim 90^\circ$. The IXPE observations give us completely new information about the properties of the neutron star surface and magnetosphere and lend further support to the presence of the quantum mechanical effect of vacuum birefringence.