X-ray polarization study of the neutron star low-mass X-ray binary GX 349+2

TL;DR

This study presents the first X-ray polarimetric measurements of the neutron star low-mass X-ray binary GX 349+2, revealing polarization properties that inform the accretion geometry and emission components of the system.

Contribution

First X-ray polarimetric analysis of GX 349+2, providing insights into its accretion geometry and emission regions using IXPE and NuSTAR data.

Findings

Detected polarization degree of 1.1% with a polarization angle of 32 degrees.

Identified spectral components including accretion disk, NS surface, and Comptonized emission.

Observed the source transitioning through different Z-track states during observations.

Abstract

We report the first X-ray polarimetric results of the neutron star (NS) low-mass X-ray binary (LMXB) Z-source GX 349+2 using the Imaging X-ray Polarimetry Explorer (IXPE). We discovered that the X-ray source was polarized at PD = 1.1 +/- 0.3% (1-sigma errors) with a polarization angle of PA = 32 +/- 6 degree (1-sigma errors). Simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR) observations show that the source transitioned through the normal branch (NB), flaring branch (FB), and soft apex (SA) of the Z-track during our IXPE observations. The X-ray spectro-polarimetry results suggest a source geometry comprising an accretion disk component, a blackbody representing the emission from the NS surface, and a Comptonized component. We discuss the accretion geometry of the Z source in light of the spectro-polarimetric results.