Browsing by Subject "galaxies: active"

Now showing items 1-10 of 18

    • Constraints on the gamma-ray emission from the cluster-scale AGN outburst in the hydra A galaxy cluster 

      Abramowski, A.; Büsching, I.; Casanova, S.; Pekeur, N.W.; Sheidaei, F.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2012)
      Context. In some galaxy clusters, powerful active galactic nuclei (AGN) have blown bubbles with cluster scale extent into the ambient medium. The main pressure support of these bubbles is not known to date, but cosmic rays ...

    • 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. ...

    • Discovery of VHE y-ray emission and multi-wavelength observations of the BL Lacertae object 1RXS J101015.9-311909 

      Abramowski, A.; Büsching, I.; Casanova, S.; De Jager, O.C.; Pekeur, N.W.; Sheidaei, F.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Science, 2012)
      1RXS J101015.9 − 311909 is a galaxy located at a redshift of z = 0.14 hosting an active nucleus (called AGN) belonging to the class of bright BL Lac objects. Observations at high (HE, E > 100 MeV) and very high (VHE, E > ...

    • Flux upper limits for 47 AGN observed with H.E.S.S. in 2004-2011 

      Abramowski, A.; Casanova, S.; Davids, I.D.; Krüger, P.P.; Pekeur, N.W.; Sushch, I.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2014)
      Context. About 40% of the observation time of the High Energy Stereoscopic System (H.E.S.S.) is dedicated to studying active galactic nuclei (AGN), with the aim of increasing the sample of known extragalactic very-high-energy ...

    • Hadronic models of blazars require a change of the accretion paradigm 

      Zdziarski, Andrzej A.; Böttcher, Markus (Oxford University Press, 2015)
      We study hadronic models of broad-band emission of jets in radio-loud active galactic nuclei, and their implications for the accretion in those sources. We show that the models that account for broad-band spectra of blazars ...

    • HESS and Fermi-LAT discovery of γ-rays from the blazar 1ES 1312-423 

      Abramowski, A.; Casanova, S.; Krüger, P.P.; Pekeur, N.W.; Sushch, I.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (Oxford Univ Press, 2013)
      A deep observation campaign carried out by the High Energy Stereoscopic System (HESS) on Centaurus A enabled the discovery of γ-rays from the blazar 1ES 1312−423, 2° away from the radio galaxy. With a differential flux at ...

    • HESS observations and VLT spectroscopy of PG 1553+113 

      Aharonian, F.; Büshing, I.; De Jager, O.C.; Holleran, M.; Raubenheimer, B.C.; Venter, C.; H.E.S.S. Collaboration (EDP Sciences, 2008)
      Aims.The properties of the very high energy (VHE; GeV) γ-ray emission from the high-frequency peaked BL Lac PG 1553+113 are investigated. An attempt is made to measure the currently unknown redshift of this object. Methods.VHE ...

    • The high-energy γ-ray emission of AP Librae 

      Abramowski, A.; Böttcher, M.; Casanova, S.; Davids, I.D.; Krüger, P.P.; Pekeur, N.W.; Sushch, I.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2015)
      The γ-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 GeV) γ-ray emission up to the TeV range by the H.E.S.S. experiment. This ...

    • Long-term monitoring of PKS2155-304 with ATOM and H.E.S.S.: investigation of optical/y-ray correlations in different spectral states 

      Abramowski, A.; Böttcher, M.; Davids, I.D.; Ivascenko, A.; Krüger, P.P.; Pekeur, N.W.; Spanier, F.; Sushch, I.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2014)
      In this paper we report on the analysis of all the available optical and very high-energy y-ray (>200 GeV) data for the BL Lac object PKS 2155-304, collected simultaneously with the ATOM and H.E.S.S. telescopes from ...

    • Magnetic field amplification and flat spectrum radio quasars 

      Chen, Xuhui; Böttcher, Markus; Chatterjee, Ritaban; Zhang, Haocheng; Pohl, Martin (Oxford University Press, 2014)
      We perform time-dependent, spatially resolved simulations of blazar emission to evaluate several flaring scenarios related to magnetic-field amplification and enhanced particle acceleration. The code explicitly accounts ...