Now showing items 1-10 of 26

    • The 2010 very high energy γ-ray flare and 10 years of multi-wavelength observations of M 87 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Sheidaei, F.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (IOP Publishing, 2012)
      The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3 – 6) × 109 M☉) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) γ-ray ...
    • 3C 279 in outburst in 2015 june: a broadband sed study based on the integral detection 

      Bottacini, Eugenio; Böttcher, Markus; Pian, Elena; Collmar, Werner (IOP Publishing, 2016)
      Blazars radiate from radio through gamma-ray frequencies and thereby make ideal targets for multifrequency studies. Such studies allow the properties of the emitting jet to be constrained. 3C 279 is among the most notable ...
    • Cascading constraints from neutrino-emitting blazars: the case of TXS 0506+056 

      Reimer, Anita; Böttcher, Markus; Buson, Sara (IOP Publishing, 2019)
      We present a procedure to generally constrain the environments of neutrino-producing sites in photomeson production models of jetted active galactic nuclei (AGNs) where any origin of the dominant target photon field can ...
    • Characterizing the γ-ray long-term variability of PKS 2155-304 with H.E.S.S. and Fermi-LAT 

      Abdalla, H.; Barnard, M.; Böttcher, M.; Davids, I.D.; Garrigoux, T.; Ivascenko, A.; Krüger, P.P.; Pekeur, N.W.; Seyffert, A.S.; Spanier, F.; Sushch, I.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; H.E.S.S. Collaboration (EDP Sciences, 2017)
      Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To ...
    • Discovery of hard-spectrum y-ray emission from the BL Lacertae object 1ES 0414+009 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Sheidaei, F.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2012)
      Context. 1ES 0414 + 009 (z = 0.287) is a distant high-frequency-peaked BL Lac object, and has long been considered a likely emitter of very-high-energy (VHE, E > 100 GeV) γ-rays due to its high X-ray and radio flux. Aims. ...
    • EBL inhomogeneity and hard-spectrum gamma-ray sources 

      Abdalla, Hassan; Böttcher, Markus (IOP Publishing, 2017)
      The unexpectedly hard very-high-energy (VHE; E > 100 GeV) γ-ray spectra of a few distant blazars have been interpreted as evidence of a reduction of the γγ opacity of the universe due to the interaction of VHE γ-rays with ...
    • Energy loss in intergalactic pair beams: particle-in-cell simulation 

      Kempf, A.; Kilian, P.; Spanier, F. (EDP Sciences, 2016)
      Aims. The change in the distribution function of electron-positron pair beams determines whether GeV photons can be produced as secondary radiation from TeV photons. We will discuss the instabilities driven by pair ...
    • Gamma-gamma absorption in the broad line region radiation fields of gamma-ray blazars 

      Böttcher, Markus; Els, Paul (IOP Publishing, 2016)
      The expected level of γγ absorption in the Broad Line Region (BLR) radiation field of γ-ray loud Flat Spectrum Radio Quasars (FSRQs) is evaluated as a function of the location of the γ-ray emission region. This is done ...
    • H.E.S.S. discovery of very high energy γ-ray emission from PKS 0625−354 

      Abdalla, H.; Barnard, M.; Davids, I.D.; Garrigoux, T.; Ivascenko, A.; Pekeur, N.W.; Seyffert, A.S.; Spanier, F.; Sushch, I.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; H.E.S.S. Collaboration (Oxford Univ Press, 2018)
      PKS 0625−354 (z = 0.055) was observed with the four High Energy Stereoscopic System (H.E.S.S.) telescopes in 2012 during 5.5 h. The source was detected above an energy threshold of 200 GeV at a significance level of 6.1σ. ...
    • A hard gamma-ray flare from 3C 279 in 2013 December 

      Paliya, Vaidehi S.; Diltz, Chris; Böttcher, Markus; Stalin, C.S.; Buckley, David (IOP, 2016)
      The blazar 3C 279 exhibited twin γ-ray flares of similar intensity in 2013 December and 2014 April. In this work, we present a detailed multi-wavelength analysis of the 2013 December flaring event. Multi-frequency observations ...