Two-zone model as origin of hard gamma-rays spectrum in extreme BL Lacs

TL;DR

This paper introduces a two-zone leptohadronic model with external radiation fields to explain the hard gamma-ray spectra of extreme BL Lac objects, successfully fitting the spectral energy distribution of 1ES 0229+200.

Contribution

The work presents a novel two-zone leptohadronic model incorporating external radiation fields to explain extreme BL Lac gamma-ray spectra, addressing limitations of previous one-zone models.

Findings

Model successfully reproduces the spectral energy distribution of 1ES 0229+200.

Photopion process in the inner blob explains TeV gamma-ray emission.

Outer blob accounts for X-ray and sub-TeV gamma-ray emission.

Abstract

The emission of the so-called extreme blazars challenges the particle acceleration models. The hardness of its spectrum, $<2$, demands extreme parameters using the standard one-zone SSC model in the high energy band. Some authors use both two-zone or hadronic/leptohadronic models to relax these extreme values. In this work, we present a leptohadronic two-zone model with external radiation fields to explain the broadband emission, where the contribution of two components forms the hard-spectrum in the $\gamma$-rays band. The first is produced by the photopion process, where accelerated protons in an inner blob located close to the core interact with the X-ray photons coming from a pair plasma. This mechanism will be responsible for $\gamma$-rays in the TeV's energies range. The second contribution is produced by an outer blob, which corresponds to the source of X-rays and $\gamma$-rays with sub-TeV energies via the standard SSC and EIC model. We exemplify our model with the prototype extreme blazar 1ES 0229 +200 obtaining a good description of its spectral energy distribution.