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

Abstract

The first source catalog of Large High Altitude Air Shower Observatory reported the detection of a very-high-energy gamma ray source, 1LHAASO J1219+2915. In this paper a further detailed study of the spectral and temporal behavior of this point-like source have been carried. The best-fit position of the TeV source ($\mathrm{RA}=185.05^{\circ }\pm 0.04^{\circ }$, $\mathrm{Dec}=29.25^{\circ }\pm 0.03^{\circ }$) is compatible with NGC 4278 within $\sim 0.03$ degree. Variation analysis shows an indication of the variability at a few months level 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 AGN NGC 4278. The observations by LHAASO-WCDA during active period has a significance level of 8.8\,$\sigma$ with best-fit photon spectral index $\Gamma =2.56\pm 0.14$ and a flux $f_{1-10\mathrm{TeV}}=(7.0\pm 1.1_{\mathrm{sta}}\pm 0.35_{\mathrm{syst}})\times 10^{-13}\mathrm{photons}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$, or approximately $5\%$ of the Crab Nebula. The discovery of VHE from NGC 4278 indicates that the compact, weak radio jet can efficiently accelerate particles and emit TeV photons.

arXiv comment11 pages, 5 figures

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• Multiple Emission Regions in Jets of Low Luminosity Active Galactic Nucleus in NGC 4278
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• Jet formation studies in AGN: a search for new targets
• TeV Gamma-Rays from the Low-Luminosity Active Galactic Nucleus NGC 4278: Implications for the Diffuse Neutrino Background
• Interpreting Swift and NuSTAR Observations of the Low-Luminosity Active Galactic Nucleus NGC 4278 with Radiatively Inefficient Accretion Flows and Implications for Neutrino Emission
• Physical origin of very-high-energy gamma rays from the low-luminosity active galactic nucleus NGC 4278 and implications for neutrino observations