Multiple Emission Regions in Jets of Low Luminosity Active Galactic Nucleus in NGC 4278

TL;DR

This paper models radio emission in the jets of NGC 4278, a low-luminosity active galactic nucleus, and suggests a separate high-energy component is responsible for gamma-ray emission detected by LHAASO.

Contribution

It introduces a multi-component model explaining gamma-ray emission in NGC 4278, highlighting a distinct high-energy emission region in the jets.

Findings

Radio components are larger than the high-energy component.

Synchrotron and SSC emissions cannot explain the gamma-ray data.

A separate high-energy component is needed to fit multi-wavelength observations.

Abstract

The Large High Altitude Air Shower Observatory (LHAASO) has detected very high energy gamma rays from the LINER galaxy NGC 4278, which has a low luminosity active galactic nucleus, and symmetric mildly relativistic S-shaped twin jets detected by radio observations. Few low-luminosity active galactic nuclei are detected in gamma rays due to their faintness. Earlier, several radio-emitting components were detected in the jets of NGC 4278. We model their radio emission with synchrotron emission of ultra-relativistic electrons to estimate the strength of the magnetic field inside these components within a time-dependent framework after including the ages of the different components. We show that the synchrotron and synchrotron self-Compton emission by these components cannot explain the Swift X-ray data and the LHAASO gamma-ray data from NGC 4278. We suggest that a separate component in one of the jets is responsible for the high energy emission whose age, size, magnetic field and the spectrum of the ultra-relativistic electrons inside it have been estimated after fitting the multi-wavelength data of NGC 4278 with the sum of the spectral energy distributions from the radio components and the high energy component. We note that the radio components of NGC 4278 are larger than the high-energy component which has also been observed in several high-luminosity active galactic nuclei.