Speaker
Description
Pulsar wind nebulae (PWNe) seem to be the most common gamma-ray sources in recent surveys of the very-high-energy and ultra-high-energy sky (with HESS, HAWC, or LHAASO). They are formed by the interaction of a relativistic pulsar wind with the stellar ejecta of the parent supernova remnant (SNR). Electron-positron pairs accelerated in the vicinity of the pulsar and diffusing away across the shocked pulsar wind nebula produce spatially and spectrally extended emission through the synchrotron and inverse-Compton scattering radiation processes.
Over the past decades, developments in gamma-ray observations and data analysis techniques have revealed very extended sources and/or multiple emission component in gamma-ray sources coincident with powerful pulsars. This is hard to reconcile with simple model predictions for PWNe, which are commonly performed under the assumption that the parent SNR expands in a uniform interstellar medium (ISM). Moreover, in many cases, the parent SNR is not detected, casting further doubt on such a description of the SNR evolution. Yet, pulsars are born from massive stars, whose powerful winds excavate large cavities around them. Supernovae explode in such stratified wind-blown bubbles (WBBs) that drastically differ from the uniform average ISM.
We investigated how this environment affects the development of an SNR-PWN system. We performed a series of numerical experiments in which we implemented a 1D hydrodynamical analog of a SNR-PWN system and followed its evolution inside a WBB. This revealed many fundamental differences in the SNR and PWN evolutions, in terms of spatial extent, dynamics, energy content, and thermal X-ray signature. In advanced stages, those expected to characterise many gamma-ray PWNe, both the SNR and the PWN are larger by factors of a few, and the former emits very little thermal X-rays while the latter holds much more energy. Our findings therefore provide a convenient explanation for the above-mentioned observational puzzles.
