Physical Origin of Very-high-energy Gamma Rays from the Low-luminosity Active Galactic Nucleus NGC 4278 and Implications for Neutrino Observations

2026/01/31 by Shilong Chen, Abhishek Das, B. Theodore Zhang +3
Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Astrophysical Phenomena and Observations #Astrophysical jet #Astrophysics and Cosmic Phenomena #Doppler effect #Galaxy #Gamma ray #Gamma-ray bursts and supernovae #Luminosity #Neutrino #Photon #Spectral energy distribution #astro-ph.GA #astro-ph.HE

paper · pdf · doi:10.3847/1538-4357/ae7c67

published as The Astrophysical Journal, 1007:10 (2026) · 10 pages, 8 figures, 5 tables, Published in The Astrophysical Journal

openalex publication_date 2026/07/31 · openalex created_date 2026/08/01 · openalex updated_date 2026/08/02 · arxiv created 2026/08/04 · arxiv updated 2026/08/05

Abstract

Abstract Relativistic jets in active galactic nuclei (AGNs) are known to accelerate particles to extreme energies, yet the physical origin of very-high-energy (VHE) emission from low-luminosity (LL) AGNs remains unclear. NGC 4278, a nearby LL AGN, has recently been identified as a VHE source following detections by LHAASO. In this work, we present a multiwavelength and multimessenger analysis to investigate the origin of this emission. Swift X-Ray Telescope monitoring reveals a quasi-quiescent state characterized by the low X-ray flux. Modeling the broadband spectral energy distribution with the leptohadronic code AMES , we find that a standard one-zone synchrotron self-Compton model underpredicts the VHE flux, unless a relatively high Doppler factor ( δ ≳ 6) is invoked. Alternatively, an external inverse-Compton (EIC) scenario—scattering seed photons from a radiatively inefficient accretion flow—provides a good description of the broadband emission with modest jet power and Doppler factor. We further explore neutrino production within a leptohadronic framework. The EIC model in the quasi-quiescent state yields the largest predicted number of muon neutrinos, reaching <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>0.001</mml:mn> </mml:math> over 15 yr of IceCube observations (assuming that 0.1% of the Eddington luminosity is converted into high-energy protons). Future multimessenger observations are essential to unveil the details of the high-energy processes of NGC 4278.

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