A Pulsar Wind Nebula Origin of the Ultra-high-energy Source 1LHAASO J1929+1846

Abstract

1LHAASO J1929+1846 is one of the ultra-high-energy (UHE, E > 0.1 PeV) sources in the first catalog of γ-ray sources detected by the Large High Altitude Air Shower Observatory. It has been detected fluxes at 3 TeV for 2.48 ± 0.11 × 10−13 TeV−1 cm−2 s−1 with the Water Cherenkov Detector Array and at 50 TeV for 0.64 ± 0.06 × 10−16 TeV−1 cm−2 s−1 with the Kilometer Squared Array, but the origin of its UHE emission remains unknown. The pulsar wind nebula (PWN) G54.1+0.3, which is powered by the pulsar PSR 1930+1852 with a period of 136 ms and it is detected within a 0.°29 region around the centroid of 1LHAASO J1929+1846. We explore whether G54.1+0.3 is capable of producing the UHE radiation of 1LHAASO J1929+1846. First, the data with Fermi Large Area Telescope for the PWN is analyzed to obtain the GeV fluxes. Second, the multiband non-thermal fluxes for the nebula are investigated based on a one-zone time-dependent model. In the model, we assume the spin-down energy of the pulsar is persistently injected into particles (electrons and positrons) and magnetic field in the PWN, and these high-energy particles produce multiband non-thermal radiation from radio to γ-rays via synchrotron radiation and inverse Compton scattering. We reproduce the spectral energy distribution of PWN G54.1+0.3 with reasonable parameters. The result indicates that the UHE γ-ray source 1LHAASO J1929+1846 possibly originates from PWN G54.1+0.3.