Magnetic field geometry of the gamma-ray binary PSR B1259-63 revealed via X-ray polarization

TL;DR

This study presents the first measurement of X-ray polarization in the gamma-ray binary PSR B1259-63, revealing the magnetic field's orientation in the particle acceleration region during a specific orbital phase.

Contribution

It provides the first X-ray polarization measurement of a gamma-ray binary, offering new insights into magnetic field geometry in pulsar-stellar wind collision zones.

Findings

X-ray polarization degree of 8.3% detected

Polarization angle aligned with shock cone axis

Magnetic field oriented perpendicular to shock cone axis

Abstract

Some X-ray binaries containing an energetic pulsar in orbit around a normal star accelerate particles to high energies in the shock cone formed where the pulsar and stellar winds collide. The magnetic field geometry in the acceleration region in such binaries is unknown. We performed the first measurement of the polarization of the X-ray synchrotron emission from a gamma-ray emitting binary system. We observed PSR B1259-63 with the Imaging X-ray Polarimetry Explorer (IXPE) during an X-ray bright phase following the periastron passage in June 2024. X-ray polarization is detected with a polarization degree of $8.3\% \pm 1.5\%$ at a significance of $5.3 \sigma$. The X-ray polarization angle is aligned with the axis of the shock cone at the time of the observation. This indicates that the predominant component of the magnetic field in the acceleration region is oriented perpendicular to the shock cone axis.