Monitoring of the FSRQ PKS 1510-089 with H.E.S.S

TL;DR

This study presents extensive multiwavelength monitoring of the FSRQ PKS 1510-089 with H.E.S.S., revealing complex variability and challenging simple correlation models across different energy bands.

Contribution

First detailed multiwavelength analysis of PKS 1510-089 at VHE, showing complex behavior and lack of clear correlations, suggesting diverse emission processes.

Findings

No obvious correlation between VHE and other bands.

Active in multiple frequency bands over long periods.

Complex flaring behavior complicates theoretical interpretation.

Abstract

The flat spectrum radio quasar (FSRQ) PKS 1510-089 (z=0.361) is known for its complex multiwavelength behavior. It has been monitored regularly at very high energy (VHE, $E>100\,$GeV) gamma-rays with H.E.S.S. since its discovery in 2009 in order to study the unknown behavior of FSRQs in quiescence at VHE, as well as the flux evolution around flaring events. Given the expected strong cooling of electrons and the absorption of VHE emission within the broad-line region, a detection of PKS 1510-089 at VHE in a quiescent state would be an important result, implying an acceleration and emission region on scales beyond the broad-line region. The H.E.S.S. monitoring has been intensified since 2015 and is complemented by monitoring at high energy ($E>100\,$MeV) gamma-rays with Fermi, at X-rays with Swift-XRT, and at optical frequencies with ATOM. The dense lightcurves allow for the first time detailed comparison studies between these energy bands. The source has been active in several frequency bands for a large fraction of the observation time frames. Yet, we do not find obvious correlations between the VHE and the other bands over the observed time frame indicating a non-trivial interplay of the acceleration, cooling and radiative processes. It also implies a rich variety in flaring behavior, which makes this source difficult to interpret within a unique theoretical framework.