Discovery of an extended GeV counterpart to the TeV source 1LHAASO J1945+2424 in Fermi-LAT data

With almost 15 yr of data taken by the Large Area Telescope (LAT) onboard the Fermi satellite we discovered an extended source of GeV emission in the region of the very high energy (TeV) source 1LHAASO J1945+2424. This TeV source is more extended than the LAT source. The spectrum of the GeV emission is hard (with a photon spectral index ~1.5) and connects smoothly with that of the TeV source, indicating a likely common origin. In order to explain the origin of the γ-rays we explore scenarios that are typically used for supernova remnants (SNRs) and pulsar wind nebulae (PWNe). For an SNR with a single particle population, a leptonic particle distribution in the form of a broken power law with a break energy of ~3.7 TeV explains the spectra well, while in the hadronic scenario a simple power law with a hard spectral index of ~1.64 is necessary. In the PWN scenario, reasonable parameters are obtained for a source age of 10 kyr and current pulsar spin-down luminosity of ~10³⁴ erg s^-1.