Astronomers study mysterious ultra-high-energy gamma-ray source LHAASO J2108+5157

Significance map of the LHAASO J2108+5157 region using ∼ 2400 days of data taken by HAWC. Credit: Kumar et al., 2023.

A team of astronomers from the University of Maryland and Michigan Technological University conducted research on a very high-energy gamma-ray source, known as LHAASO J2108+5157. These sources emit gamma radiation with photon energies above 0.1 PeV, classified as ultra-high energy (UHE) gamma ray sources. The nature of these sources is poorly understood, leading scientists to search for new objects of this type. LHAASO J2108+5157 is a point source with dimensions less than 0.39 degrees. It lies about 10,700 light-years away and is associated with a molecular cloud called [MML2017]4607. Previous observations have found no X-ray equivalent to this gamma-ray source, making it difficult to determine the origin of its emissions. To continue their research, astronomers used the High-Energy Radiation Imaging Telescope System (VERITAS) and the High Altitude Cherenkov Observatory (HAWC) to observe LHAASO J2108+5157. However, these observations indicate no significant emissions near the source location. Therefore, the researchers performed spectral analysis in the surrounding area, which yielded an upper limit of the differential current consistent with previous studies. This suggests a lepton origin of the emission with energies ranging from a few TeV to hundreds of TeV. Interestingly, the recent identification of a new molecular cloud near LHAASO J2108+5157 indicates that gamma rays may be produced by a hadronic channel, with the molecular cloud serving as the primary target for the Cosmic ray particles accelerated by unknown PeVatrons. Further observations and analyzes in the X-ray range are needed to fully understand the nature of this mysterious source of extremely high energy. The researchers emphasize the importance of future Cherenkov Telescope Array (CTA) observations to gather more information about LHAASO J2108+5157.