The high-energy $\gamma$-ray emission of AP Librae

Abstract

The $\gamma$-ray spectrum of the low-frequency-peaked BL Lac (LBL) object AP Librae is studied, following the discovery of very-high-energy (VHE; $E>100\mathrm{GeV}$) $\gamma$-ray emission up to the TeV range by the H.E.S.S. experiment. This makes AP Librae one of the few VHE emitters of the LBL type. The measured spectrum yields a flux of $(8.8\pm 1.5_{\mathrm{stat}}\pm 1.8_{\mathrm{sys}})\times 10^{-12}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ above 130 GeV and a spectral index of $\Gamma =2.65\pm 0.19_{\mathrm{stat}}\pm 0.20_{\mathrm{sys}}$. This study also makes use of \textit{Fermi}-LAT, observations in the high energy (HE, E$>$100 MeV) range, providing the longest continuous light curve (5 years) ever published on this source. The source underwent a flaring event between MJD 56306-56376 in the HE range, with a flux increase of a factor 3.5 in the 14-day bin light curve and no significant variation in spectral shape with respect to the low-flux state. While the H.E.S.S., and (low state) \textit{Fermi}-LAT fluxes are in good agreement where they overlap, a spectral curvature between the steep VHE spectrum and the \textit{Fermi}-LAT, spectrum is observed. The maximum of the $\gamma$-ray emission in the spectral energy distribution is located below the GeV energy range.

15 pages, 6 figures

References in corpus (7)

• Observations of the Crab Nebula with H.E.S.S
• Fermi Large Area Telescope Bright Gamma-ray Source List
• Bright AGN Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey
• MAGIC discovery of VHE Emission from the FSRQ PKS 1222+21
• Background Modelling in Very-High-Energy gamma-ray Astronomy
• Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects
• Discovery of very high energy gamma-ray emission from the low-frequency peaked BL Lacertae object BL Lacertae

Cited by in corpus (5)

• Linking radio and gamma ray emission in Ap Librae
• The TeV emission of Ap Librae: a hadronic interpretation and prospects for CTA
• Searches for correlation between UHECR events and high-energy gamma-ray Fermi-LAT data
• Constraints on Proton Synchrotron Origin of Very High Energy Gamma Rays from the Extended Jet of AP Librae
• Attenuation of TeV $\gamma$-rays by the starlight photon field of the host galaxy