2025ApJ...987...63A

Synchrotron X-ray emission from a pulsar wind nebula (PWN) is a sensitive probe of its magnetic field and high-energy particle population. Here we analyze contemporaneous NuSTAR and XMM-Newton observations of the PWN G54.1+0.3, powered by pulsar PSR J1930+1852. We also present a preliminary timing analysis of the central pulsar PSR J1930+1852 and analyze its X-ray pulse profiles in different energy bands. We detect X-ray emission from the combined pulsar and PWN system up to ≈70 keV, while emission from the PWN itself has been detected up to ≈30 keV, with a photon index Γ increasing from ∼1.9 to ∼2.4 with photon energy between 3 and 30 keV. PWN G54.1+0.3's X-ray spectrum is consistent with a broken power law, with break energy E_break ≈ 5 keV, consistent with synchrotron cooling of a single power-law particle spectrum. The best-fit broadband spectral energy distribution model after the inclusion of this new spectral data indicates a maximum particle energy ${E}_{{\rm{\max }}}\sim $ 400 TeV. We discuss PSR J1930+1852 and PWN G54.1+0.3 in the context of other PWNe powered by young energetic pulsars.