# 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; $E>100\,{\rm GeV}$) $\gamma$-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 $(8.8 \pm 1.5_{\rm stat} \pm 1.8_{\rm sys}) \times 10^{-12}\ {\rm cm}^{-2} {\rm s}^{-1}$ above 130 GeV and a spectral index of $\Gamma = 2.65\pm0.19_{\rm stat}\pm0.20_{\rm sys}$. 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.
Document type :
Journal articles

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Contributor : Claudine Bombar <>
Submitted on : Friday, November 14, 2014 - 12:02:34 PM
Last modification on : Thursday, January 7, 2021 - 5:56:02 PM

### Citation

A. Abramowski, A. Fiasson, N. Komin, F. Krayzel, G. Lamanna, et al.. The high-energy $\gamma$-ray emission of AP Librae. Astronomy and Astrophysics - A&A, EDP Sciences, 2015, 573, pp.A31. ⟨10.1051/0004-6361/201321436⟩. ⟨in2p3-01082768⟩

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