Exploring the physics of pulsar wind nebulae with very-high-energy gamma-ray observations

Pulsar wind nebulae (PWNe) are ionized structures fueled by energetic pulsars. They produce electromagnetic emissions across a wide energy range from infrared to gamma-ray regime. The detection of several PWNe candidates by LHAASO and HAWC at photon energies above 100 TeV implies that charged particles are accelerated to the PeV range. Understanding the PWN evolution, the magnetic field within the PWN, and the particle transportation, is critical to the study of the acceleration mechanism. These questions can be answered by studying the emissions produced by the accelerated electrons through synchrotron radiation and inverse-Compton scattering, which provide information about the spatial and spectral distributions of the electrons. VERITAS is a ground-based Imaging Atmospheric Cherenkov Telescopes (IACT) sensitive to gamma rays in the energy range from 85 GeV to 30 TeV. The excellent angular and energy resolutions of IACTs allow detailed energy-dependent morphology studies to reveal particle diffusion processes and interactions between the sources and surrounding materials. We present the results of VERITAS analysis of MGRO J1908+06 emission, a PWN candidate powered by the pulsar PSR J1907+0602, which has a characteristic age of 19.5 kyr and a distance of 3.2 kpc. This mid-aged and near-distant source provides an opportunity to understand the acceleration mechanism within the PWN by studying spectral features and morphology. Furthermore, VERITAS is conducting follow-up programs to cover more LHAASO sources and PeVatron candidates, as well as a plan for PWN survey to study these energetic sources in different evolution stages. Finally, we will discuss the future CTA observatory and how this new instrument will advance our understanding of PWN physics.