Swift-XRT Observations and Upper Limits at Five LHAASO Galactic Sources

Abstract The detection of low-energy counterparts to gamma-ray sources is critical to understanding the nature of the astrophysical systems producing such high-energy emission. We report on Swift-XRT observations at five LHAASO gamma-ray sources with no known low-energy counterpart and scant previous X-ray observations. At four of the five LHAASO targets, we detect no significant X-ray point sources, while at 1LHAASO J1928+1813u we detect a single X-ray source that is likely related to X-ray emission from a local cool stellar system. These results suggest that many X-ray counterparts to LHAASO sources have X-ray flux below ≈10 −13 erg s −1 cm −2 , or have diffuse X-ray emission not visible in brief observations.