Presentation #201.07 in the session Recent Advances in Pulsar Wind Nebulae.
LHAASO has recently detected 14 Galactic gamma-ray sources capable of accelerating cosmic rays to PeV energies or greater, answering the long-sought question of whether Galactic PeVatrons exist. To move forward and identify the physical nature of these Galactic PeVatrons, we direct our attention to pulsar wind nebulae (PWNe). As leptonic particle accelerators, PWNe are bubbles of relativistic electrons and positrons formed around pulsars. Pulsar wind particles are accelerated at the termination shock to hundreds of TeV or even PeV and lose their energy through radiation, advection, and diffusion. Therefore, studying the emission spectrum and morphology of a PWN over a wide range of wavelengths provides tight constraints on its energetics and surroundings. We report the first NuSTAR observation of four PeVatron candidate PWNe spatially coincident with LHAASO sources: G75.2+0.1 (Dragonfly), G18.5-0.4 (Eel), G106.6+2.9 (Boomerang), and G32.64+0.53. We combine the NuSTAR data with new and archival VERITAS and HAWC data to model the multi-wavelength SED of the four PWNe. Based on the best-fit model parameters, such as maximum particle energy, magnetic field, and the true age of the system, we deduce common features of the PWNe. We investigate their association with the LHAASO sources and discuss the optimal astrophysical environment for PeVatrons.