From radio to TeV: the surprising spectral energy distribution of AP Librae

• Published in: Monthly notices of the Royal Astronomical Society 2015-12, Vol.454 (3), p.3229-3239
• Main Authors: Sanchez, D. A., Giebels, B., Fortin, P., Horan, D., Szostek, A., Fegan, S., Baczko, A.-K., Finke, J., Kadler, M. L., Kovalev, Y. Y., Lister, M. L., Pushkarev, A. B., Savolainen, T.
• Format: Article
• Language: English
• Subjects: ASTRONOMY AND ASTROPHYSICS; Astrophysics; BL lacertae objects: individual: AP librae; Electromagnetics; Flux; Frequencies; galaxies: active; galaxies: jets; High Energy Astrophysical Phenomena; Object recognition; Octaves; Physics; Radio; Radio astronomy; Radio sources (astronomy); Spectral energy distribution; Spectrum analysis; Symbols; Synchrotrons
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stv2151

Following the discovery of high-energy (HE; E > 10 MeV) and very-high-energy (VHE; E > 100 GeV) γ-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 (non-simultaneous) γ-ray data are used to construct the most precise spectral energy distribution of this source. The data have been found to be modelled with difficulties with single-zone homogeneous leptonic synchrotron self-Compton (SSC) radiative scenarios due to the unprecedented width of the HE component when compared to the lower-energy component. The two other LBL objects also detected at VHE appear to have similar modelling difficulties. Nevertheless, VHE γ-rays produced in the extended jet could account for the VHE flux observed by HESS.