Observations of a UHE-Only Source: LHAASO J2027+3657 and its Potential Counterpart

LHAASO J2027+3657 is an ultra-high-energy (UHE) gamma-ray extended source discovered by LHAASO in the Cygnus region. No significant gamma-ray emission with energy below 10 TeV has been detected from this source, and ground-based facilities like H.E.S.S. and HAWC have not detected it either, making the origin of its emission especially interesting. In this study, we use the latest LHAASO data to perform a detailed analysis of the morphology and spectrum of LHAASO J2027+3657. The morphology of the source exhibits a particularly elongated shape, and we achieved higher significance by fitting the source using an elliptical template. The potential candidate counterparts in the extended region have been investigated. Additionally, we correlate molecular clouds in the source direction using data from the Milky Way Imaging Scroll Painting (MWISP) project, examine observations from Fermi-LAT and X-ray instruments, and discuss possible emission mechanisms based on these results.