Browsing by Subject "gamma rays: galaxies"

Now showing items 1-10 of 16

    • Discovery of TeV y-ray emission from PKS 0447-439 and derivation of an upper limit on its redshift 

      Abramowski, A.; Casanova, S.; Krüger, P.P.; Pekeur, N.W.; Sheidaei, F.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2013)
      Very high-energy γ-ray emission from PKS 0447−439 was detected with the H.E.S.S. Cherenkov telescope array in December 2009. This blazar is one of the brightest extragalactic objects in the Fermi bright source list and has ...

    • Discovery of very high energy γ-ray emission from the BL Lacertae object PKS 0301-243 with H.E.S.S. 

      Abramowski, A.; Böttcher, M.; Casanova, S.; Krüger, P.P.; Pekeur, N.W.; Sushch, I.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2013)
      The active galactic nucleus PKS 0301−243 (z = 0.266) is a high-synchrotron-peaked BL Lac object that is detected at high energies (HE, 100 MeV < E < 100 GeV) by Fermi/LAT. This paper reports on the discovery of PKS 0301−243 ...

    • 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 ...

    • Investigating broadband variability of the TeV blazar IES 1959+650 

      Aliu, E.; Böttcher, M.; Archambault, S.; Arlen, T.; Aune, T. (IOP Publishing, 2014)
      We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift Ultraviolet and Optical ...

    • Leptonic and hadronic modeling of Fermi-detected blazars 

      Böttcher, M.; Reimer, A.; Sweeney, K.; Prakash, A. (IOP Science, 2013)
      We describe new implementations of leptonic and hadronic models for the broadband emission from relativistic jets in active galactic nuclei in a temporary steady state. For the leptonic model, a temporary equilibrium between ...

    • 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 ...

    • Multiwavelength observations and modeling of 1ES 1959+650 in low flux state 

      Aliu, E.; Böttcher, M.; Archambault, S.; Arlen, T.; Aune, T. (IOP Science, 2013)
      We report on the VERITAS observations of the high-frequency peaked BL Lac object 1ES 1959+650 in the period 2007–2011. This source is detected at TeV energies by VERITAS at 16.4 standard deviation (σ) significance in 7.6 ...

    • A multiwavelength view of the flaring state of PKS 2155-304 in 2006 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2012)
      Context: Multiwavelength (MWL) observations of the blazar PKS 2155-304 during two weeks in July and August 2006, the period when two exceptional flares at very high energies (VHE, E ≳ 100 GeV) occurred, provide a detailed ...

    • The polarization dependence of γγ absorption - implications for γ-ray bursts and blazars 

      Böttcher, M. (IOP Publishing, 2014)
      This paper presents an analysis of the dependence of the opacity for high-energy γ-rays to γγ absorption by low-energy photons on the polarization of the γ-ray and target photons. This process has so far only been considered ...

    • Radio to gamma-ray variability study of blazar S5 0716+714 

      Rani, B.; Böttcher, M.; Krichbaum, T.P.; Fuhrmann, L.; Lott, B. (EDP Sciences, 2013)
      We present the results of a series of radio, optical, X-ray, and γ-ray observations of the BL Lac object S50716+714 carried out between April 2007 and January 2011. The multifrequency observations were obtained using several ...