PKS 1510-089: a rare example of a flat spectrum radio quasar with a very high-energy emission

TL;DR

This paper models the spectral energy distribution of blazar PKS 1510-089 during high-energy flares, revealing that infrared photons from the dusty torus significantly contribute to very high-energy emissions, challenging previous assumptions.

Contribution

The study applies a single-zone internal shock model to successfully reproduce the multiwavelength spectrum, including very high-energy emissions, of PKS 1510-089, incorporating external photon sources and gamma-ray absorption effects.

Findings

High-energy emission results from Comptonization of infrared photons from the dusty torus.

The model explains the detection of very high-energy photons despite Klein-Nishina suppression.

External photon fields and gamma-ray absorption are crucial in modeling blazar spectra.

Abstract

The blazar PKS 1510-089 is an example of flat spectrum radio quasars. High-energy emissions from this class of objects are believed to have been produced by inverse Compton radiation with seed photons originating from the broad line region. In such a paradigm, a lack of very high-energy emissions is expected because of the Klein-Nishina effect and strong absorption in the broad line region. Recent detection of at least three such blazars by Cherenkov telescopes has forced a revision of our understanding of these objects. We have aimed to model the observed spectral energy distribution of PKS 1510-089 from the high-energy flares in March 2009, during which very high-energy emission were also detected by H.E.S.S. We have applied the single-zone internal shock scenario to reproduce the multiwavelength spectrum of PKS~1510-089. We have followed the evolution of the electrons as they propagate along the jet and emit synchrotron and inverse Compton radiation. We have considered two sources of external photons: the dusty torus and the broad line region. We have also examined the effects of the gamma-gamma absorption of the high-energy photons both in the AGN environment (the broad line region and the dusty torus), as well as while traveling over cosmological distances: the extragalactic background light. We have successfully modeled the observed spectrum of PKS 1510-089. In our model, the highest energy emission is the result of the Comptonization of the infrared photons from the dusty torus, thus avoiding Klein-Nishina regime, while the bulk of the emissions in the GeV range may still be dominated by the Comptonization of radiation coming from the broad line region.