TeV Emission in NGC 4278: Shock Energetics Insufficient, Compact Origin Favored

Abstract The Large High Altitude Air Shower Observatory recently detected TeV emission from the low-luminosity active galactic nucleus (LLAGN) NGC 4278. Integral-field spectroscopy with MEGARA revealed ionized outflows on hundred-parsec scales with kinetic power <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>˙</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">shock</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>38</mml:mn> </mml:mrow> </mml:msup> </mml:math> erg s −1 , well below the TeV luminosity L γ ≳ 10 41 erg s −1 . The implied efficiencies, η ≳ 1000, are far above unity, showing that shocks cannot account for the TeV emission. Contemporaneous Fermi-Large Area Telescope and Swift data, consistent with a compact synchrotron self-Compton jet component, favor a nuclear origin. NGC 4278 is the first low-ionization nuclear emission-line region (LINER)/LLAGN of its class detected at TeV energies, a benchmark for LINERs with outflows and a prime target for the Cherenkov Telescope Array Observatory. I conclude that the TeV photons arise from a compact nuclear accelerator, while optical outflows trace larger-scale jet–ISM interactions that coexist but do not power the TeV radiation.