Spectro-polarimetric study of the black hole X-ray binary Swift J1727.8-1613 in the JED-SAD framework
Abstract
Context. Swift J1727.8-1613 is an X-ray binary observed during its 2023-2024 outburst, including bright and dim hard states with similar X-ray polarimetric signatures but fluxes differing by two orders of magnitude. Aims. We aim to reproduce the spectro-polarimetric properties of these two hard states. Methods. We modelled their spectra in the JED-SAD framework and computed the X-ray polarisation properties of the best-fit configurations with the MONK general relativistic radiative transfer code. Results. Both spectra are well reproduced within the JED-SAD framework, although the dominant radiative process differs: self-Comptonised bremsstrahlung in the bright state and self-Comptonised synchrotron in the dim state. In the bright state, the simulated polarisation fraction remains below the observed value of about 4%, while the polarisation angle differs from the observations by 90 degrees because of the JED's large vertical optical depth. In contrast, the dim state's simulated polarisation fraction is about 3% and its polarisation angle is perpendicular to the disk, both broadly consistent with IXPE measurements. The dim-state results are largely insensitive to the magnetic field configuration because of Faraday depolarisation. Conclusions. The dim hard state's spectro-polarimetric properties are well reproduced, whereas those of the bright state are not. We discuss a non-thermal particle distribution and electron scattering in an accretion-disk wind as possible explanations for the observed bright-state polarisation.
Related
- The compact jets of the black hole X-ray binary Swift J1753.5-0127 during its 2023-2024 outburst
- The broad-band X-ray spectral properties during the rising phases of the outburst of the new black hole X-ray binary candidate Swift J1727.8–1613
- Multiwavelength View of Black Hole X-ray Binary Swift J151857.0-572147
- Spectropolarimetric detection of baryonic mass loading in a transient relativistic jet: application to the black hole X-ray binary Swift J1727.8−1613
- A unified modeling of X-ray and gamma-ray spectro-polarimetric data: the case of Cygnus X-1
BibTeX
@misc{muhammad2026spectropolarimetric,
title = {{Spectro-polarimetric study of the black hole X-ray binary Swift J1727.8-1613 in the JED-SAD framework}},
author = {R Muhammad and P.-O Petrucci and W Zhang and J Ferreira and R Belmont and J Malzac and G Marcel and G Matt and M Parra and T Bouchet and N Barnier and M Clavel and G Henri},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.15301},
eprint = {2609.15301},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05782749v1},
note = {CC0},
}
RIS
TY - UNPB
TI - Spectro-polarimetric study of the black hole X-ray binary Swift J1727.8-1613 in the JED-SAD framework
AU - R Muhammad
AU - P.-O Petrucci
AU - W Zhang
AU - J Ferreira
AU - R Belmont
AU - J Malzac
AU - G Marcel
AU - G Matt
AU - M Parra
AU - T Bouchet
AU - N Barnier
AU - M Clavel
AU - G Henri
PY - 2026
DA - 2026/09/14
PB - HAL
DO - 10.48550/arxiv.2609.15301
UR - https://hal.science/hal-05782749v1
AB - Context. Swift J1727.8-1613 is an X-ray binary observed during its 2023-2024 outburst, including bright and dim hard states with similar X-ray polarimetric signatures but fluxes differing by two orders of magnitude. Aims. We aim to reproduce the spectro-polarimetric properties of these two hard states. Methods. We modelled their spectra in the JED-SAD framework and computed the X-ray polarisation properties of the best-fit configurations with the MONK general relativistic radiative transfer code. Results. Both spectra are well reproduced within the JED-SAD framework, although the dominant radiative process differs: self-Comptonised bremsstrahlung in the bright state and self-Comptonised synchrotron in the dim state. In the bright state, the simulated polarisation fraction remains below the observed value of about 4%, while the polarisation angle differs from the observations by 90 degrees because of the JED's large vertical optical depth. In contrast, the dim state's simulated polarisation fraction is about 3% and its polarisation angle is perpendicular to the disk, both broadly consistent with IXPE measurements. The dim-state results are largely insensitive to the magnetic field configuration because of Faraday depolarisation. Conclusions. The dim hard state's spectro-polarimetric properties are well reproduced, whereas those of the bright state are not. We discuss a non-thermal particle distribution and electron scattering in an accretion-disk wind as possible explanations for the observed bright-state polarisation.
ER -