Discovery of Very-high-energy Gamma-ray Emissions from the Low Luminosity AGN NGC 4278 by LHAASO

The first source catalog of the Large High Altitude Air Shower Observatory (LHAASO) reported the detection of a very high energy gamma-ray source, 1LHAASO J1219+2915. This Letter presents a further detailed study of the spectral and temporal behavior of this pointlike source. The best-fit position of the TeV source (R.A. = 185.degrees 05 +/- 0.degrees 04, decl. = 29.degrees 25 +/- 0.degrees 03) is compatible with NGC 4278 within similar to 0.degrees 03. Variation analysis shows an indication of variability on a timescale of a few months in the TeV band, which is consistent with low-frequency observations. Based on these observations, we report the detection of TeV gamma-ray emissions from this low-luminosity active galactic nucleus. The observation by LHAASO's Water Cherenkov Detector Array during the active period has a significance level of 8.8 sigma with a best-fit photon spectral index Gamma = 2.56 +/- 0.14 and a flux f(1-10 TeV) = (7.0 +/- 1.1(sta) +/- 0.35(syst)) x 10(-13) photons cm(-2) s(-1), or approximately 5% of the Crab Nebula. The discovery of VHE gamma-ray emission from NGC 4278 indicates that compact, weak radio jets can efficiently accelerate particles and emit TeV photons.