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Physical origin of very-high-energy gamma rays from the low-luminosity active galactic nucleus NGC 4278 and implications for neutrino observations
High Energy Astrophysical Phenomena · Submitted 30 Jan 2026
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim 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.
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The abstract, sentence by sentence
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 ($\delta \gtrsim 6$) 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 $N_{\nu_{\mu}} \sim 0.001$ 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.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | 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. | gap 0.58 | 0.04 | 0.03 | asserted 0.96 |
| s1 | NGC 4278, a nearby LL AGN, has recently been identified as a VHE source following detections by LHAASO. | background 0.90 | 0.08 | 0.03 | asserted 1.00 |
| s2 | In this work, we present a multiwavelength and multimessenger analysis to investigate the origin of this emission. | contribution 0.99 | 0.82 | 0.03 | asserted 0.83 |
| s3 | Swift X-Ray Telescope monitoring reveals a quasi-quiescent state characterized by the low X-ray flux. | result 0.79 | 0.82 | 0.02 | asserted 1.00 |
| s4 | 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 ($\delta \gtrsim 6$) is invoked. | result 0.99 | 0.95 | 0.14 | asserted 1.00 |
| s5 | 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. | result 0.92 | 0.86 | 0.35 | asserted 0.93 |
| s6 | We further explore neutrino production within a leptohadronic framework. | contribution 0.83 | 0.88 | 0.03 | asserted 0.55 |
| s7 | The EIC model in the quasi-quiescent state yields the largest predicted number of muon neutrinos, reaching $N_{\nu_{\mu}} \sim 0.001$ over 15 yr of IceCube observations (assuming that 0.1\% of the Eddington luminosity is converted into high-energy protons). | result 1.00 | 0.91 | 0.30 | asserted 0.94 |
| s8 | Future multimessenger observations are essential to unveil the details of the high-energy processes of NGC 4278. | future work 1.00 | 0.06 | 0.07 | asserted 0.82 |
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The paper
Original 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 ($\delta \gtrsim 6$) 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 $N_{\nu_{\mu}} \sim 0.001$ 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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References
How the literature uses it
1 arXiv paper cite this in 1 sentence
Papers citing it
Cites it as background 1 paper
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For the corona model, no Doppler boosting is assumed[While this paper was under review, two other publications discussing leptohadronic models appeared on the arXiv, both within an outflow scenario [ref] ].
VERITAS Observations Contemporaneous with the LHAASO Detection of NGC 4278 · Hadronic interactions · 0.89
What it cites · 12 sentences without a confident label
Uses the method or tool of 4 papers
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For this work, we perform an unbinned likelihood analysis, following the methodology of previous IceCube point-source searches [ref] to evaluate the significance of a potential neutrino signal originating from the direction of NGC 4278.
Methods for point source analysis in high energy neutrino telescopes · Neutrino Observations · 1.00
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For this work, we perform an unbinned likelihood analysis, following the methodology of previous IceCube point-source searches [ref] to evaluate the significance of a potential neutrino signal originating from the direction of NGC 4278.
2101.09836 · Neutrino Observations · 1.00
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In this work, we mainly solve Equation [ref] and [ref] using the AGN module of AMES [ref] .
Hidden Hearts of Neutrino Active Galaxies · Particle transport and radiative processes · 0.98
Uses data or values from 6 papers
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The source exhibits distinct activity states: a flaring state with an integrated luminosity of $L_0.1-10 TeV ∼3.0×10^41 erg s^-1$, and a quasi-quiescent state with $L_0.1-10 TeV ∼4.3×10^40 erg s^-1$ [ref] .
2405.07691 · VHE Gamma-ray Observations · 1.00
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Based on the measured radio core luminosity, the jet power is estimated to be $P_jet ∼(1-2)×10^42 erg s^-1$ [ref] .
A relationship between AGN jet power and radio power · Introduction · 0.95
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Based on the measured radio core luminosity, the jet power is estimated to be $P_jet ∼(1-2)×10^42 erg s^-1$ [ref] .
The two sided parsec scale structure of the Low Luminosity Active Galactic Nucleus in NGC 4278 · Introduction · 0.95
Compares with 4 papers
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Our fitting results are generally consistent with those of [ref] and [ref] , though our derived emission region radius is smaller by a factor of approximately five.
Origin of the Very High Energy {\gamma}-rays in the Low-luminosity Active Galactic Nucleus NGC 4278 · Flaring State · 1.00
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The total power of the two-sided jet is $P_jet ≃2.5 ×10^41 erg s^-1$, which is lower than the jet kinetic energy derived from radio measurements [ref] .
The two sided parsec scale structure of the Low Luminosity Active Galactic Nucleus in NGC 4278 · Flaring State · 0.83
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Our choice of jet power is rather conservative, comparing the neutrino emission modeling in blazars [ref] , where the jet power close to the Eddington luminosity is often adopted.
Diffuse Neutrino Intensity from the Inner Jets of Active Galactic Nuclei: Impacts of External Photon Fields and the Blazar Sequence · Leptohadronic model · 0.92
Cites as background 5 papers
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Recently, [ref] proposed that these gamma-rays originate from $pp$ interactions of escaped cosmic rays (CRs).
2507.02326 · Introduction · 0.85
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In addition to pure leptonic processes, VHE gamma rays can be also produced from protons, including proton synchrotron emission, decay of neutral pions, and associated cascade emission from the $pp$ and $pγ$ processes [ref] .
Leptonic and Hadronic Modeling of Fermi-Detected Blazars · Leptohadronic model · 0.94
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In addition to pure leptonic processes, VHE gamma rays can be also produced from protons, including proton synchrotron emission, decay of neutral pions, and associated cascade emission from the $pp$ and $pγ$ processes [ref] .
A Multimessenger Picture of the Flaring Blazar TXS 0506+056: implications for High-Energy Neutrino Emission and Cosmic Ray Acceleration · Leptohadronic model · 0.94
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