2026ApJ...997..213X

HESS J1809-193 is an unassociated very-high-energy γ-ray source located in the Galactic plane. The source with a distinctive morphology and spectrum has an extension of 0$\mathop{.}\limits^{\unicode{x000b0}}$62 with a compact component (r ≤ 0$\mathop{.}\limits^{\unicode{x000b0}}$1). To explain its multiwavelength emission, we develop a self-consistent, spatially dependent, multizone leptonic model. The system is assumed to be spherically symmetric, with electrons injected near the pulsar termination shock and their subsequent evolution described by a Fokker-Planck-type transport equation. The evolution of the electrons includes convection, diffusion, adiabatic losses, and radiative losses. With suitable parameters, the model reproduces the observed multiwavelength fluxes of HESS J1809-193 reasonably well. The fit indicates that the compact component shows well-developed synchrotron and inverse Compton emission characteristics of a pulsar wind nebula (PWN), whereas the extension exhibits a halo-like morphology without a corresponding synchrotron counterpart, suggesting that the source is transitioning from a PWN to a TeV halo.