From Radio to TeV: The surprising Spectral Energy Distribution of AP Librae

TL;DR

This paper presents a comprehensive spectral energy distribution of AP Librae across 60 energy octaves, revealing modeling challenges with standard leptonic scenarios and suggesting extended jet VHE emission as a possible explanation.

Contribution

It provides the most detailed SED of AP Librae and highlights the difficulties of single-zone models, proposing extended jet emission as an alternative explanation.

Findings

Spectral energy distribution spans 60 energy octaves.

Single-zone leptonic models struggle to fit the data.

Extended jet VHE emission could explain observed gamma rays.

Abstract

Following the discovery of high-energy (HE; $E>10\,{\rm MeV}$) and very-high-energy (VHE; $E>100\,{\rm GeV}$) $\gamma$-ray emission from the low-frequency-peaked BL~Lac (LBL) object AP Librae, its electromagnetic spectrum is studied over 60 octaves in energy. Contemporaneous data in radio, optical and UV together with the $\gamma$-ray data are used to construct the most precise spectral energy distribution of this source. The data have been found to be modeled with difficulties with single zone homogeneous leptonic synchrotron self-Compton (SSC) radiative scenarios due to the unprecedented width of the high-energy component when compared to the lower-energy component. The two other LBL objects also detected at VHE appear to have similar modeling difficulties. Nevertheless, VHE $\gamma$ rays produced in the extended jet could account for the VHE flux observed by H.E.S.S.