2024A&A...681A..34D

Context. The Large High Altitude Air Shower Observatory (LHAASO) has detected multiple ultra-high-energy (UHE; E_γ ≥ 100 TeV) gamma-ray sources in the Milky Way Galaxy, which are associated with Galactic “PeVatrons” that accelerate particles up to PeV (=10¹⁵ eV) energies. Although supernova remnants (SNRs) and pulsar wind nebulae (PWNe), as source classes, are considered the leading candidates, further theoretical and observational efforts are needed to find conclusive proof that can confirm the nature of these PeVatrons.
Aims. The aim of this work is to provide a phenomenological model to account for the emission observed from the direction of LHAASO J0341+5258, an unidentified UHE gamma-ray source observed by LHAASO. Further, we also aim to provide the implications of our model in order to support future observations at multiple wavelengths.
Methods. We analyzed 15 yr of Fermi-LAT data to find the high-energy (HE; 100 MeV ≤ E_γ ≤ 100 GeV) GeV gamma-ray counterpart of LHAASO J0341+5258 in the 4FGL-DR3 catalog. We explain the spectrum of the closest 4FGL source, 4FGL J0340.4+5302, by a synchro-curvature emission formalism. We explored the escape-limited hadronic interaction between protons accelerated in an old, now invisible SNR and cold protons inside associated molecular clouds (MCs) and leptonic emission from a putative TeV halo in an effort to explain the multiwavelength (MWL) spectral energy distribution (SED) observed from the LHAASO source region.
Results. The spectrum of 4FGL J0340.4+5302 is explained well by the synchro-curvature emission, which, along with its point-like nature, indicates that this object is likely a GeV pulsar. A combined lepto-hadronic emission from SNR+MC and TeV halo scenarios explains the MWL SED of the LHAASO source. In addition, we find that leptonic emission from an individual TeV halo is also consistent with the observed MWL emission. We discuss possible observational avenues that can be explored in the near future and predict the outcome of those observational efforts from the model explored in this paper.