X-ray and radio polarimetry of the neutron star low mass X-ray binary GX 13+1

TL;DR

This study combines X-ray and radio polarimetry to analyze the geometry and emission components of the neutron star low-mass X-ray binary GX 13+1, revealing insights into its accretion disk and boundary layer structure.

Contribution

It provides the first simultaneous X-ray and radio polarization measurements of GX 13+1, elucidating its source geometry and emission regions.

Findings

X-ray dips are associated with polarization swings.

The source has a geometry with an accretion disk and boundary layer.

Polarization data suggest specific emission regions.

Abstract

We report the X-ray and radio polarization study of the neutron star (NS) low-mass X-ray binary (LMXB) GX 13+1 using the Imaging X-ray Polarimetry Explorer (IXPE) and Very Large Array (VLA). Simultaneous Neutron Star Interior Composition Explorer (NICER) observations show that the source was in parts of the Z state during our IXPE observations, exhibiting moderate changes in the hardness intensity diagram. The source exhibits X-ray dips in the light curve along with hints of polarization swings between the dip and non-dip states. The X-ray spectro-polarimetry results suggest a source geometry comprising an accretion disk component representing the softer disk emission, along with a blackbody representing the harder emission from the boundary layer (BL) or a spreading layer (SL). We investigate the geometry of GX 13+1 by considering our X-ray and radio polarization findings.