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

A. Abramowski , A. Fiasson (1) , N. Komin (1) , F. Krayzel (1) , G. Lamanna (1) , G. Maurin (1) , S. Rosier-Lees (1) , D.A. Sanchez (1) , C. Trichard (1) , J. Biteau (2) , B. Degrange (2) , S. Fegan (2) , G. Fontaine (2) , B. Giebels (2) , M. De Naurois (2) , D. Horan (2) , J. Bolmont (3) , R. Chalme-Calvet (3) , M. Chétien (3) , C. Couturier (3) , T. Garrigoux (3) , A. Jacholkowska (3) , Michel Kieffer (3) , J.-P. Lenain (3) , C.L. Naumann (3) , J.-P. Tavernet (3) , P. Vincent (3) , M. Dalton (4) , H. Laffon (4) , M. Lemoine-Goumard (4) , J. Méhault (4) , A. Djannati-Ataï (5) , P. Espigat (5) , B. Khélifi (5) , J. Lefaucheur (5) , A. Lemière (5) , S. Pita (5) , M. Punch (5) , I. Reichardt (5) , T. Tavernier (5) , F. Feinstein (6) , D. Fernandez (6) , Y.A. Gallant (6) , Alexandre Marcowith (6) , Matthieu Renaud (6) , George Vasileiadis (6) , Catherine Boisson (7) , Olivier Hervet (7) , Cameron Rulten (7) , Régis Terrier (5) , Andreas Zech (7) , Helene Sol (7)

1 LAPP - Laboratoire d'Annecy de Physique des Particules
2 LLR - Laboratoire Leprince-Ringuet
3 LPNHE (UMR_7585) - Laboratoire de Physique Nucléaire et de Hautes Énergies
4 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan
5 APC (UMR_7164) - AstroParticule et Cosmologie
6 LUPM - Laboratoire Univers et Particules de Montpellier
7 LUTH (UMR_8102) - Laboratoire Univers et Théories

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.

Domaines: Phénomènes cosmiques de haute energie [astro-ph.HE]

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, 2015, 573, pp.A31. ⟨10.1051/0004-6361/201321436⟩. ⟨in2p3-01082768⟩