Speaker
Description
We report the first detection of TeV $\gamma$-ray emission from the region of the evolved supernova remnant (SNR) Simeis 147 (S147; G180.0$-$1.7) and its associated pulsar PSR J0538+2817, using 1484 days of LHAASO-WCDA observations and 1944 days of LHAASO-KM2A observations. The emission exhibits a clear energy-dependent morphology: the WCDA data favor a compact source plus an extended Gaussian component, whereas the KM2A emission above 25 TeV is consistent with a single compact source. A joint analysis resolves the emission into the compact source LHAASO J0538+2829 and the degree-scale extended source LHAASO J0539+2802. LHAASO J0538+2829 lies only $0.21^\circ$ from PSR J0538+2817 and is aligned with a recently discovered one-sided radio filament extending ahead of the pulsar. Accounting for both the source-localization uncertainty and this directional alignment, we estimate a local chance-coincidence probability of $0.34\%$, which decreases to $0.06\%$ for pulsars with $\dot{E}/d^2>10^{34}\ {\rm erg\,s^{-1}\,kpc^{-2}}$, favoring a pulsar-related origin. No significant 10 GeV--1 TeV counterpart is detected at the compact-source position, while XMM-Newton observations also yield only an upper limit, constraining leptonic models and implying $B\lesssim16~\mu{\rm G}$ for the adopted electron spectrum. For the extended component, an analysis of 18 years of Fermi-LAT data together with MWISP $^{12}$CO, CGPS $\mathrm{H\,I}$, and H$\alpha$ observations favors a CO+disk morphology. The GeV disk is separated from the gas-correlated emission and lies only $0.19^\circ$ from LHAASO J0539+2802, with its spectrum connecting naturally to the TeV measurements. These results reveal at least two physically distinct high-energy components in S147: a compact, likely pulsar-powered source possibly produced by collimated outflow or anisotropic particle escape, and an extended GeV--TeV component associated with the SNR environment.
