Spatially-resolved Evolutionary Emission Model for Pulsar Wind Nebulae

Pulsar wind nebulae are bubbles of electron/positron/B plasma supplied by energetic pulsars. It is believed that the electrons are accelerated to high energies at the termination shocks of the PWNe. Therefore, PWNe are recognized as an efficient particle accelerator generating high-energy cosmic rays. This is supported by the detections of hard X-rays and ultra high-energy (>100 TeV) photons from some sources. Additionally, it is known that PWNe cause the mysterious halos around old pulsars. Particle acceleration and flow within PWNe are crucial in comprehending the nature of TeV halos and high-energy electrons/positrons detected on Earth. The properties of the PWNe can be inferred from broadband observations in the radio to TeV band, since they emit radiation across the entire electromagnetic waveband. While these observational studies can provide qualitative understanding of PWNe, quantitative models are necessary to deepen our insight. For this, we constructed a spatially-resolved evolutionary emission model, which is capable of explaining not only the spectral energy distributions (SEDs) but also spatially varying spectra of PWNe. The model considers spatial as well as temporal variation of the PWNe properties such as magnetic field strength and the flow speed, which are affected by the surrounding environment (ISM, background photons) and the pulsar. In this presentation, we provide details on the construction of the model, and computation of the evolution of the PWN and particles in it. We applied this model to several PWN systems to explain the observed SED, surface brightness profile, and photon index profile.