Observations of SNR CTB 109 with LHAASO

CTB 109 is a middle-aged shell-type supernova remnant (SNR) with bright thermal X-ray emission. The gamma-ray emission of CTB 109 exhibits a center-bright morphology, which is very consistent with its thermal X-ray emission rather than the shell-type structure in the radio band. The GeV gamma-ray spectrum shows a significant spectral curvature at a few GeV, which can well explain the lack of TeV gamma-ray emission from CTB 109. In this work, we describe the observations of CTB 109 by LHAASO, together with the updated observations by Fermi-LAT. Based on the LHAASO measurements, we will set stringent upper limits on the distribution of particles accelerated by CTB 109. We perform extensive modelling using multi-wavelength data available for CTB 109, and discuss the different emission models for leptonic and hadronic scenarios.