Herschel PACS and SPIRE observations of blazar PKS 1510-089: a case for two blazar zones

TL;DR

This study uses Herschel and multiwavelength data to analyze blazar PKS 1510-089, revealing that a two-zone model explains its emission better than a one-zone model, with different regions responsible for infrared and gamma-ray emissions.

Contribution

The paper introduces a two-zone blazar model that accounts for multiwavelength observations, challenging the traditional one-zone leptonic model for PKS 1510-089.

Findings

Infrared emission linked to hot-dust region at supra-pc scale

Gamma-ray emission associated with broad-line region at sub-pc scale

One-zone model cannot explain the observed spectral features

Abstract

We present the results of observations of blazar PKS 1510-089 with the Herschel Space Observatory PACS and SPIRE instruments, together with multiwavelength data from Fermi/LAT, Swift, SMARTS and SMA. The source was found in a quiet state, and its far-infrared spectrum is consistent with a power-law with a spectral index of alpha ~ 0.7. Our Herschel observations were preceded by two 'orphan' gamma-ray flares. The near-infrared data reveal the high-energy cut-off in the main synchrotron component, which cannot be associated with the main gamma-ray component in a one-zone leptonic model. This is because in such a model the luminosity ratio of the External-Compton and synchrotron components is tightly related to the frequency ratio of these components, and in this particular case an unrealistically high energy density of the external radiation would be implied. Therefore, we consider a well-constrained two-zone blazar model to interpret the entire dataset. In this framework, the observed infrared emission is associated with the synchrotron component produced in the hot-dust region at the supra-pc scale, while the gamma-ray emission is associated with the External-Compton component produced in the broad-line region at the sub-pc scale. In addition, the optical/UV emission is associated with the accretion disk thermal emission, with the accretion disk corona likely contributing to the X-ray emission.