Broadband Modeling of Low-luminosity Active Galactic Nuclei Detected in Gamma Rays

Abstract

Low-luminosity active galactic nuclei are more abundant and closer to us than the luminous ones but harder to explore as they are faint. We have selected the four sources, NGC 315, NGC 4261, NGC 1275, and NGC 4486, which have been detected in gamma-rays by Fermi-LAT. We have compiled their long-term radio, optical, X-ray data from different telescopes, and analyzed XMM-Newton data for NGC 4486 and XMM-Newton and Swift data for NGC 315. We have analyzed the Fermi-LAT data collected over the period of 2008 to 2020 for all of them. Electrons are assumed to be accelerated to relativistic energies in subparsec-scale jets, which radiate by synchrotron and synchrotron self-Compton emission covering radio to gamma-ray energies. This model can fit most of the multiwavelength data points of the four sources. However, the gamma-ray data points from NGC 315 and NGC 4261 can be well fitted only up to 1.6 GeV and 0.6 GeV, respectively, in this model. This motivates us to find out the origin of the higher-energy gamma-rays detected from these sources. Kiloparsec-scale jets have been observed previously from these sources in radio and X-ray frequencies. If we assume gamma-rays are also produced in kiloparsec-scale jets of these sources from inverse-Compton scattering of starlight photons by ultrarelativistic electrons, then it is possible to fit the gamma-ray data at higher energies. Our result also suggests that strong host galaxy emission is required to produce GeV radiation from kiloparsec-scale jets.