Simulations of high-energy emission from high-mass microquasars via jet–wind interaction

Graduate Institute of Communication Engineering, National Taiwan University, Taipei 10617, Taiwan

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Received: 21 October 2024
Accepted: 19 October 2025

Abstract

Context. A jet bursting from a high-mass microquasar (HMMQ) behaves just as its scaled-down counterpart bursting from an active galactic nucleus. The jet–wind interaction is conjectured to affect the γ-ray emission. A jet in a HMMQ evolves much faster than its counterpart in an AGN, making the former valuable in studying accretion, eruption, and emission processes around a black hole.

Aims. The plasma dynamics and high-energy emission of a relativistic magnetized jet immersed in a stellar wind were studied via simulations. The values of relevant parameters were estimated from observation data, and the simulated spectrum is similar to that of Cygnus X-1 in the Fermi observation.

Methods. A self-consistent relativistic magnetohydrodynamics (RMHD) model was developed to simulate the plasma evolution by taking into account the interaction among the relativistic jet, stellar wind, and magnetic field. The high-energy emissions out of jet–wind interaction via synchrotron radiation and inverse Compton scattering were analyzed by taking a post-processing approach. This model and its simulations results will be very useful in explaining many observed features and predicting more complicated scenarios in the future.

Results. The jet dynamics, radiation map, flux orbital variability, spectrum of radiation flux, and photon index are justified with consistent models and validated wherever possible with the available observation data. The simulation results indicate that a shock front is induced by the relativistic jet, followed by a rarefied region with lower mass density and gas pressure. The magnetic field manifests a petal-like shape over the jet region. The emission patterns at various photon energies indicate that synchrotron radiation dominates at lower energy and inverse Compton scattering dominates at higher energy. The difference in radiation flux observed at different azimuth angles ϕ_i results in flux orbital variability, which is characterized by photon indices of Γ = 2.38, 2.34, and 2.36 at ϕ_i = −π/2, 0, and π/2, respectively. The fine features of high-energy emissions, not available in the observation, are manifested as useful clues for future studies.