Browsing Research Output by Author "Abramowski, A."

Now showing items 21-40 of 46

    • H.E.S.S. observations of the globular clusters NGC 6388 and M15 and search for a dark matter signal 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (IOP Publishing, 2011)
      Observations of the globular clusters (GCs) NGC 6388 and M15 were carried out by the High Energy Stereoscopic System array of Cherenkov telescopes for a live time of 27.2 and 15.2 hr, respectively. No gamma-ray signal is ...

    • 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 J1640-465: an exceptionally luminous TeV γ-ray supernova remnant 

      Abramowski, A.; Casanova, S.; Davids, I.D.; Krüger, P.P.; Pekeur, N.W.; Sushch, I.; Venter, C.; Vorster, M.; Böttcher, M.; H.E.S.S. Collaboration (Oxford Univ Press, 2014)
      The results of follow-up observations of the TeV γ-ray source HESS J1640−465 from 2004 to 2011 with the High Energy Stereoscopic System (HESS) are reported in this work. The spectrum is well described by an exponential ...

    • HESS J1818-154, a new composite supernova remnant discovered in TeV gamma rays and X-rays 

      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, 2014)
      Composite supernova remnants (SNRs) constitute a small subclass of the remnants of massive stellar explosions where non-thermal radiation is observed from both the expanding shell-like shock front and from a pulsar wind ...

    • HESS observations of the Carina nebula and its enigmatic colliding wind binary Eta Carinae 

      Abramowski, A.; Büsching, I.; Casanova, S.; Pekeur, N.W.; Sheidaei, F.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (Oxford Univ Press, 2012)
      The massive binary system Eta Carinae and the surrounding HII complex, the Carina nebula, are potential particle acceleration sites from which very high energy (VHE; E ≥ 100 GeV) γ -ray emission could be expected. This ...

    • Identification of HESS J1303-631 as a pulsar wind nebula through y-ray, x-ray, and radio observations 

      Abramowski, A.; Büsching, I.; Casanova, S.; Pekeur, N.W.; Sheidaei, F.; Venter, C.; Vorster, M. (EDP Science, 2012)
      Aims. The previously unidentified very high-energy (VHE; E > 100 GeV) γ-ray source HESS J1303−631, discovered in 2004, is re-examined including new data from the H.E.S.S. Cherenkov telescope array in order to identify 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 ...

    • Long-term TeV and X-ray observations of the gamma-ray binary HESS J0632+057 

      Abramowski, A.; Böttcher, M.; Casanova, S.; Krüger, P.P.; Pekeur, N.W.; Sushch, I.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (IOP Publishing, 2014)
      HESS J0632+057 is the only gamma-ray binary known so far whose position in the sky allows observations with ground-based observatories in both the northern and southern hemispheres. Here we report on long-term observations ...

    • Measurement of the extragalactic background light imprint on the spectra of the brightest blazars observed with H.E.S.S. 

      Abramowski, A.; Casanova, S.; Pekeur, N.W.; Sheidaei, F.; Venter, C.; Vorster, M. (EDP Sciences, 2013)
      The extragalactic background light (EBL) is the diffuse radiation with the second highest energy density in the Universe after the cosmic microwave background. The aim of this study is the measurement of the imprint of the ...

    • Multi-wavelength observations of H 2356-309 

      Abramowski, A.; Büsching, I.; Davids, I.D.; De Jager, O.C.; Holleran, M.; Raubenheimer, B.C.; Venter, C.; H.E.S.S. Collaboration (EDP Sciences, 2010)
      Aims. The properties of the broad-band emission from the high-frequency peaked BL Lac H 2356–309 (z = 0.165) are investigated. Methods. Very high energy (VHE; E > 100 GeV) observations of H 2356–309 were performed with ...

    • 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 ...

    • A new SNR with TeV shell-type morphology: HESS J1731-347 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2011)
      Aims. The recent discovery of the radio shell-type supernova remnant (SNR), G353.6-0.7, in spatial coincidence with the unidentified TeV source HESS J1731−347 has motivated further observations of the source with the High ...

    • Probing the extent of the non-thermal emission from the Vela X region at TeV energies with H.E.S.S. 

      Abramowski, A.; Casanova, S.; Krüger, P.P.; Pekeur, N.W.; Sheidaei, F.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (EDP Sciences, 2012)
      Context. Vela X is a region of extended radio emission in the western part of the Vela constellation: one of the nearest pulsar wind nebulae, and associated with the energetic Vela pulsar (PSR B0833-45). Extended ...

    • Revisiting the Westerlund 2 field with the HESS telescope array 

      Abramowski, A.; Büsching, I.; Casanova, S.; Davids, I.D.; De Jager, O.C.; Holleran, M.; Sushch, I.; Venter, C.; H.E.S.S. Collaboration (EDP Sciences, 2011)
      Aims. Previous observations with the HESS telescope array revealed the existence of extended very-high-energy (VHE; E > 100 GeV) γ-ray emission, HESS J1023–575, coincident with the young stellar cluster Westerlund 2. At ...

    • Search for a dark matter annihilation signal from the galactic center halo with H.E.S.S. 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (APS, 2011)
      A search for a very-high-energy (VHE; ≥100  GeV) γ-ray signal from self-annihilating particle dark matter (DM) is performed towards a region of projected distance r∼45–150  pc from the Galactic center. The background-subtracted ...

    • Search for dark matter annihilation signals from the fornax galaxy cluster with HESS 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Sheidaei, F.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (IOP Publishing, 2012)
      The Fornax galaxy cluster was observed with the High Energy Stereoscopic System for a total live time of 14.5 hr, searching for very high energy (VHE; E > 100GeV) γ -rays from dark matter (DM) annihilation. No significant ...

    • Search for extended γ-ray emission around AGN with H.E.S.S. and Fermi-LAT 

      Abramowski, A.; Böttcher, M.; Davids, I.D.; Krüger, P.P.; Pekeur, N.W.; Sushch, I.; Venter, C.; H.E.S.S. Collaboration (EDP Sciences, 2014)
      Context. Very-high-energy (VHE; E > 100 GeV) γ-ray emission from blazars inevitably gives rise to electron-positron pair production through the interaction of these γ-rays with the extragalactic background light (EBL). ...

    • Search for Lorentz invariance breaking with a likelihood fit of the PKS 2155-304 flare data taken on MJD 53944 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (Elsevier, 2011)
      Several models of Quantum Gravity predict Lorentz Symmetry breaking at energy scales approaching the Planck scale (∼1019 GeV). With present photon data from the observations of distant astrophysical sources, it is possible ...

    • Search for photon line-like signatures from dark matter annihilations with H.E.S.S 

      Abramowski, A.; Casanova, S.; Krüger, P.P.; Pekeur, N.W.; Sheidaei, F.; Venter, C.; Vorster, M.; H.E.S.S. Collaboration (APS, 2013)
      Gamma-ray line signatures can be expected in the very-high-energy (VHE; E_\gamma > 100 GeV) domain due to self-annihilation or decay of dark matter (DM) particles in space. Such a signal would be readily distinguishable ...

    • Search for TeV Gamma-ray emission from GRB 100621A, an extremely bright GRB in X-rays, 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, 2014)
      The long gamma-ray burst (GRB) 100621A, at the time the brightest X-ray transient ever detected by Swift-XRT in the 0:3–10 keV range, has been observed with the H.E.S.S. imaging air Cherenkov telescope array, sensitive ...