Leptonic and Hadronic Modeling of Fermi-Detected Blazars

TL;DR

This paper develops and applies leptonic and hadronic models to fit the broadband emission spectra of Fermi-detected blazars, providing insights into jet composition and emission mechanisms.

Contribution

It introduces new steady-state leptonic and hadronic modeling methods, including a semi-analytical cascade evaluation, and applies them to real blazar data.

Findings

Leptonic models fit most blazar SEDs well with near-equipartition parameters.

Hadronic models can satisfactorily fit most SEDs but struggle with some features.

Jet kinetic energy is likely dominated by protons in leptonic models.

Abstract

We describe new implementations of leptonic and hadronic models for the broadband emission from relativistic jets in AGN in a temporary steady state. For the leptonic model, a temporary equilibrium between particle injection/acceleration, radiative cooling, and escape from a spherical emission region is evaluated, and the self-consistent radiative output is calculated. For the hadronic model, a temporary equilibrium between particle injection/acceleration, radiative and adiabatic cooling, and escape is evaluated for both primary electrons and protons. A new, semi-analytical method to evaluate the radiative output from cascades initiated by internal gamma-gamma pair production is presented. We use our codes to fit snap-shot spectral energy distributions of a representative set of Fermi-LAT detected blazars. We find that the leptonic model provides acceptable fits to the SEDs of almost all blazars with parameters close to equipartition between the magnetic field and the relativistic electron population. However, the hard gamma-ray spectrum of AO 0235+164, in contrast to the very steep IR-optical-UV continuum, poses a severe problem for the leptonic model. If charge neutrality in leptonic models is provided by cold protons, the kinetic energy carried by the jet should be dominated by protons. We find satisfactory representations of the snapshot SEDs of most blazars in our sample with the hadronic model presented here. However, in the case of two quasars the characteristic break at a few GeV energies can not be well modelled. All of our hadronic model fits require powers in relativistic protons in the range L_p ~ 1e47 - 1e49 erg/s.