X-Ray and Radio Campaign of the Z-source GX 340+0. II. The X-Ray Polarization in the Normal Branch

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.

Authors

Institutions

Publication Details

Journal
The Astrophysical Journal
Published
2026-05-11
DOI
https://doi.org/10.3847/1538-4357/ae5a27
Primary Topic
Particle Accelerators and Free-Electron Lasers
Type
preprint
Field-Weighted Citation Impact
0.00

Funders

Controls
|||
ALL TIME
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
preprint

X-Ray and Radio Campaign of the Z-source GX 340+0. II. The X-Ray Polarization in the Normal Branch

Francesco Carotenuto, Sudip Bhattacharyya, Herman L. Marshall, Yash Bhargava et al.
The Astrophysical Journal
Particle Accelerators and Free-Electron Lasers
preprint

X-Ray and Radio Campaign of the Z-source GX 340+0. II. The X-Ray Polarization in the Normal Branch

Francesco Carotenuto, Sudip Bhattacharyya, Herman L. Marshall, Yash Bhargava, Mayukh Pahari, Arvind Balasubramanian, Mason Ng, J. Homan, T. D. Russell, Deepto Chakrabarty, Aman Kaushik, Vishal Jadoliya, Liang Zhang, Swati Ravi
preprint en

Abstract

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.

The Astrophysical JournalVol. 1003(1)
Tata Institute of Fundamental Research (IN), Indian Institute of Astrophysics (IN), Chinese Academy of Sciences (CN), Astronomical Observatory of Rome (IT), University of Oxford (GB), Istituto di Astrofisica Spaziale e Fisica cosmica di Palermo (IT), Institute of High Energy Physics (CN), Eureka Scientific (US), Osservatorio Astronomico di Cagliari (IT), McGill University (CA), Massachusetts Institute of Technology (US), Indian Institute of Technology Hyderabad (IN)
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
Openalex Percentile: Top 100%
Particle Accelerators and Free-Electron Lasers
DOIOpen Access PDFOpenAlex
AI Navigator

Ask Laika to Summarize, Analyze, and Connect papers live on the map.

Summarize Papers & Methodologies

Extract key findings, datasets, and comparative methods across publications.

Benchmark Rankings & Visual Analytics

Rank top research institutions, authors, funders, topics, and journals by Field-Weighted Citation Impact (FWCI) and paper volume with instant charts.

Connect Distant Disciplines

Bridge topological clusters on the map to find hidden collaborative intersections.