Multi-wavelength Study of PeVatron Candidate Pulsar Wind Nebulae

The LHAASO collaboration has reported (Nature, May 2021) the discovery of a dozen PeVatrons in our Galaxy emitting photons up to 1.4 PeV – the highest energy photons that have ever been detected. Along with previous detections of 85 other Galactic TeV sources, this discovery marks an important step towards probing the “knee” of the cosmic ray spectrum. In particular, the majority of ultra-high-energy gamma-ray sources being located near energetic pulsars strongly suggests that pulsar wind nebulae (PWNe) are the most powerful Galactic particle accelerators.

G75.2+0.1 (“Dragonfly”) and G18.5-0.4 (“Eel”) are the PWNe of middle-aged energetic pulsars PSR J2021+3651 and PSR J1826-1256, respectively. The PWNe are associated with multiple very-high-energy (VHE) sources including LHAASO J2108+3651 (Dragonfly) and LHAASO J1825-1326 (Eel), making the PWNe PeVatron candidates. To understand the particle acceleration mechanism in the PWNe and its link to the VHE sources, we carry out a multi-wavelength study of the spectral energy distribution and morphology of the PWNe, and derive fundamental PWN parameters. In this work, we present the result of the analysis of Dragonfly and Eel using NuSTAR and Fermi-LAT data, along with archival VERITAS, HAWC, HESS and XMM-Newton data. We discuss the contribution of the PWNe to the VHE emissions and their capability as Galactic PeVatrons.