A Possible Hadronic Explanation for the Ultra-high-energy γ -Ray Emission from 1LHAASO J0056+6346u

Abstract The release of the first LHAASO catalog has marked a new era of γ -ray astronomy and promoted the search for Galactic PeVatrons. Among the currently reported ultra-high-energy (UHE; ≳100 TeV) sources, 1LHAASO J0056+6346u is a peculiar unidentified object lacking a firm association with any known accelerator despite its spatial coincidence with adjacent molecular clouds (MCs). In this work, we propose a scenario where the accelerated protons escaping from a putative supernova remnant (SNR) penetrate nearby MCs and produce the observed UHE γ -rays through inelastic pp collisions. By utilizing the Markov Chain Monte Carlo routines, we fit the γ -ray observational data and constrain key physical parameters of the system. Our fits favor a young system with a short Sedov time, characterized by an SNR age of t SNR ≃ 1.4–2.2 kyr, an SNR–cloud separation d ≃ 22–35 pc, a characteristic proton cutoff energy E c ≃ 0.4–0.5 PeV, and a cosmic-ray (CR) conversion fraction f CR ≃ 0.10–0.16. These results suggest that 1LHAASO J0056+6346u may trace a young SNR illuminating nearby molecular gas with an early escape of the accelerated protons. In addition, we calculate the accompanying neutrino fluxes and find that they are well below the sensitivities of current neutrino observatories and remain beneath the atmospheric neutrino background.