X-Ray and Radio Campaign of the Z-source GX 340+0. II. The X-Ray Polarization in the Normal Branch
Year: 2026
Type: article
Abstract: We present the first X-ray polarization measurement of the neutron star low-mass X-ray binary and Z-source, GX 340+0, in the normal branch (NB) using a 200 ks observation with the Imaging X-ray Polarimetric Explorer (IXPE). This observation was performed in 2024 August. Along with IXPE, we also conducted simultaneous observations with NICER, AstroSat, Insight-HXMT, the Australia Telescope Compact Array (ATCA), and the Giant Metrewave Radio Telescope (GMRT) to investigate the broadband spectral and timing properties in the X-ray and radio wavelengths. During the campaign, the source traced a complete Z-track during the IXPE observation but spent most of the time in the NB. We measure X-ray polarization degree (PD) of 1.3% ± 0.3% in the 2–8 keV energy band with a polarization angle (PA) of 38° ± 6°. The PD in the NB is observed to be weaker than in the horizontal branch (HB) but aligned in the same direction. The PD of the source exhibits a marginal increase with energy, while the PA shows no energy dependence. The joint spectro-polarimetric modeling is consistent with the observed X-ray polarization originating from a single spectral component from the blackbody, the Comptonized emission, or reflection feature, while the disk emission does not contribute toward the X-ray polarization. GMRT observations at 1.26 GHz during HB had a tentative detection at 4.5 ± 0.7 mJy, while ATCA observations a day later during the NB detected the source at 0.70 ± 0.05 mJy and 0.59 ± 0.05 mJy in the 5.5 and 9 GHz bands, respectively, suggesting an evolving jet structure depending on the Z-track position.
Source: The Astrophysical Journal
Institutions: Tata Institute of Fundamental Research, Osservatorio Astronomico di Cagliari, National Institute for Astrophysics, Istituto di Astrofisica Spaziale e Fisica cosmica di Palermo, Trottier Space Institute at McGill, McGill University, Indian Institute of Astrophysics, Chinese Academy of Sciences, Institute of High Energy Physics, Massachusetts Institute of Technology, Indian Institute of Technology Hyderabad, Eureka Scientific, Astronomical Observatory of Rome, University of Oxford
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Funders: National Aeronautics and Space Administration, China National Space Administration, Tata Institute of Fundamental Research, Indian Space Research Organisation, National Natural Science Foundation of China, Chinese Academy of Sciences, Nuclear Safety and Security Commission, Marshall Space Flight Center, Fonds de recherche du Québec – Nature et technologies
Award: G446572719
OpenAlex ID: W4404344887