Broadband Multiwavelength Study of LHAASO-detected Active Galactic Nuclei

Abstract

Recently, the Large High Altitude Air Shower Observatory (LHAASO) collaboration presented the first catalog of γ-ray sources using 508 days of LHAASO data, from 2021 March to 2022 September. This catalog contains four blazars and a possible LINER-type active galactic nucleus (AGN) counterpart. In this work, we establish averaged multiwavelength spectral energy distributions (SEDs) by combining data from the Fermi-Large Area Telescope, Swift, Zwicky Transient Facility, and Wide-field Infrared Survey Explorer (WISE) covering the same period as the LHAASO detection. In general, these five AGNs are found in low states at all wavelengths. To study the multiwavelength properties of these AGNs, several jet emission models, including the one-zone leptonic model, the one-zone leptonic and hadronuclear (pp) model, the one-zone proton-synchrotron model, and the spine-layer model, are applied to reproduce their averaged SEDs. We find that the one-zone leptonic model can reproduce most of the SEDs, except for the high-energy tail of the LHAASO spectra of Mrk 421 and Mrk 501. To improve the fitting, emission from pp interactions is favored in the framework of a one-zone model. The spine-layer model, which can be treated as a multizone scenario, can also provide good spectral fits. The influence of different extragalactic background light models on fitting a LHAASO energy spectrum is also discussed.