A unified modeling of X-ray and gamma-ray spectro-polarimetric data: the case of Cygnus X-1
Year: 2026
Type: preprint
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 $(2.8^{+0.6}_{-0.8}) \times 10^{2}$ 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.
Source: arXiv (Cornell University)
Institutions: University of Würzburg, European Space Agency, European Space Research and Technology Centre, Centre National de la Recherche Scientifique, Université Paris Cité, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, Astrophysique, Instrumentation et Modélisation, Unité d'Appui et de Recherche OSUPS, Laboratoire AstroParticule et Cosmologie, Friedrich-Alexander-Universität Erlangen-Nürnberg
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Award: G6151142271
OpenAlex ID: W7201866044