A unified modeling of X-ray and gamma-ray spectro-polarimetric data: the case of Cygnus X-1
Abstract
Recent X-ray and soft gamma-ray spectro-polarimetric observations of black hole X-ray binaries, such as Cygnus X-1, reveal discrepancies that challenge current models of accretion and high-energy emission. We present a general framework for broadband spectro-polarimetric modeling that simultaneously fits spectral and polarization data from independent instruments across different energy bands. The method robustly combines measurements with different energy binning and statistical significance while accounting for energy-dependent polarization mixing between model components. Applied to Cygnus X-1 over the 2 keV-2 MeV range, it provides an improved characterization of the soft gamma-ray hard-tail and constrains the optically thin synchrotron cutoff energy to (2.8+0.6−0.8) × 102 keV. We discuss the implications for non-thermal electron acceleration in the context of Bohm diffusion and synchrotron cooling, and propose a new explanation for the observed polarization misalignment based on magnetic field helicity and Doppler boosting. The framework is broadly applicable to multi-instrument spectro-polarimetric analyses.
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BibTeX
@misc{bouchet2026unified,
title = {{A unified modeling of X-ray and gamma-ray spectro-polarimetric data: the case of Cygnus X-1}},
author = {Tristan Bouchet and Thomas Siegert and Victoria Grinberg and Jérôme Rodriguez and Floriane Cangemi and Philippe Laurent and Joern Wilms},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2608.06328},
eprint = {2608.06328},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05736628v1},
}
RIS
TY - UNPB
TI - A unified modeling of X-ray and gamma-ray spectro-polarimetric data: the case of Cygnus X-1
AU - Tristan Bouchet
AU - Thomas Siegert
AU - Victoria Grinberg
AU - Jérôme Rodriguez
AU - Floriane Cangemi
AU - Philippe Laurent
AU - Joern Wilms
PY - 2026
DA - 2026/09/03
PB - HAL
DO - 10.48550/arxiv.2608.06328
UR - https://hal.science/hal-05736628v1
AB - Recent X-ray and soft gamma-ray spectro-polarimetric observations of black hole X-ray binaries, such as Cygnus X-1, reveal discrepancies that challenge current models of accretion and high-energy emission. We present a general framework for broadband spectro-polarimetric modeling that simultaneously fits spectral and polarization data from independent instruments across different energy bands. The method robustly combines measurements with different energy binning and statistical significance while accounting for energy-dependent polarization mixing between model components. Applied to Cygnus X-1 over the 2 keV-2 MeV range, it provides an improved characterization of the soft gamma-ray hard-tail and constrains the optically thin synchrotron cutoff energy to (2.8^+0.6_−0.8) × 10^2 keV. We discuss the implications for non-thermal electron acceleration in the context of Bohm diffusion and synchrotron cooling, and propose a new explanation for the observed polarization misalignment based on magnetic field helicity and Doppler boosting. The framework is broadly applicable to multi-instrument spectro-polarimetric analyses.
ER -