Optically thick, nonlocal, inhomogeneous, stationary jet model for high-energy radiation from blazars: Application to Mrk 421

TL;DR

This paper presents a comprehensive inhomogeneous jet model that explains high-energy gamma-ray production, absorption, and secondary emission in blazars, specifically applied to the nonflaring state of Mrk 421, aligning well with multiwavelength observations.

Contribution

It introduces an advanced optically thick, nonlocal jet model accounting for gamma-ray absorption and secondary pair emission, providing a better understanding of blazar spectra near the SMBH.

Findings

The model successfully reproduces Mrk 421's nonflaring spectrum.

Secondary synchrotron emission explains observed hard X-ray features.

Gamma-ray absorption leads to electron-positron pair production within the jet.

Abstract

There is an increasing number of observational evidence that very high energy gamma-rays in radio-loud active galactic nuclei are produced in the direct vicinity of a supermassive black hole (SMBH), close to the base of a relativistic jet. In the case of some blazars, the angle between the jet axis and the observer's line of sight is smaller than the angular extent of the jet. Gamma-rays that are produced close to SMBH therefore have to propagate in the nonthermal radiation of the extended jet before reaching the observer. This gamma-ray emission can be strongly absorbed in the extended jet radiation, producing a second generation of electron-positron pairs that loses energy mainly via the synchrotron process. We show that this advanced inhomogeneous jet model can explain the multiwavelength spectrum of the BL Lac object Mrk 421 in a nonflaring state for reasonable parameters of the jet and the SMBH. Moreover, we argue that synchrotron emission from the secondary electron-positron pairs, which appear as a result of absorption of gamma-rays that are produced close to the SMBH within the jet radiation, is consistent with the concave hard X-ray emission observed from Mrk 421.