Modeling the Broadband Emission and X-Ray Radial Profiles of Pulsar Wind Nebula G54.1+0.3

Abstract G54.1+0.3 is a Crab-like pulsar wind nebula (PWN) detected in the radio, X-ray, and TeV gamma-ray bands. Its X-ray photon index and surface brightness exhibit significant radial variations. Using a spatially resolved particle transport model that simultaneously reproduces the broadband spectrum and the radial profiles of the X-ray photon index and surface brightness, we investigate the magnetic field structure and particle transport properties within the nebula. Our results favor a radially decreasing magnetic field with a gradient index of 0.36. The radial softening of the photon index and the decline in surface brightness from the termination shock (TS) to the nebular boundary are primarily governed by energy-dependent particle diffusion with an index of 1/3, consistent with Kolmogorov-type turbulence, while synchrotron burn-off further modifies the X-ray radial profiles by steepening the photon index. These findings suggest that G54.1+0.3 represents a diffusion-dominated X-ray PWN, in contrast to synchrotron cooling-dominated systems such as the Crab Nebula and the Crab-like PWN 3C 58.