Now showing items 1-19 of 19

    • 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 ...
    • Constraints on the emission region of 3C 279 during strong flares in 2014 and 2015 through VHE γ-ray observations with H.E.S.S. 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Ndiyavala, H.; Schutte, H.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Żywucka, N.; H.E.S.S. Collaboration (EDP Sciences, 2019)
      The flat spectrum radio quasar 3C 279 is known to exhibit pronounced variability in the high-energy (100 MeV <  E <  100 GeV) γ-ray band, which is continuously monitored with Fermi-LAT. During two periods of high activity ...
    • First limits on the very-high energy gamma-ray afterglow emission of a fast radio burst. 

      Abdalla, H.; Barnard, M.; Böttcher, M.; Davids, I.D.; Garrigoux, T.; Ivascenko, A.; Krüger, P.P.; Pekeur, N.W.; Richter, S.; Seyffert, A.S.; Spanier, F.; Sushch, I.; Van der Walt, D.J.; Venter, C.; Van Rensburg, C.; Wadiasingh, Z.; H.E.S.S. Collaboration (EDP Sciences, 2017)
      Aims. Following the detection of the fast radio burst FRB150418 by the SUPERB project at the Parkes radio telescope, we aim to search for very-high energy gamma-ray afterglow emission. Methods. Follow-up observations in ...
    • Gamma-ray blazar spectra with H.E.S.S. II mono analysis: the case of PKS 2155-304 and PG 1553+113 

      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.; Venter, C.; Wadiasingh, Z.; H.E.S.S. Collaboration (EDP Sciences, 2017)
      Context. The addition of a 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment’s sensitivityto lower energies. The lowest energy threshold is obtained using monoscopic analysis of data taken with ...
    • H.E.S.S. and Fermi-LAT observations of PSR B1259-63/LS 2883 during its 2014 and 2017 periastron passages 

      Abdalla, H.; Arcara, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Kreter, M.; Ndiyavala, H.; Schutte, H.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Żywucka, N.; Fermi LAT; H.E.S.S. Collaboration (EDP Sciences, 2020)
      Context. PSR B1259–63/LS 2883 is a gamma-ray binary system consisting of a pulsar in an eccentric orbit around a bright Oe stellar-type companion star that features a dense circumstellar disc. The bright broad-band emission ...
    • H.E.S.S. and Suzaku observations of the Vela X pulsar wind nebula 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Ndiyavala, H.; Schutte, H.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Zywucka, N.; H.E.S.S. Collaboration (EDP Sciences, 2019)
      Context. Pulsar wind nebulae (PWNe) represent the most prominent population of Galactic very-high-energy gamma-ray sources and are thought to be an efficient source of leptonic cosmic rays. Vela X is a nearby middle-aged ...
    • H.E.S.S. observations of the flaring gravitationally lensed galaxy PKS 1830-211 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Ndiyavala, H.; Schutte, H.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; H.E.S.S. Collaboration (Oxford Univ Press, 2019)
      PKS 1830–211 is a known macrolensed quasar located at a redshift of z = 2.5. Its high-energy gamma-ray emission has been detected with the Fermi-Large Area Telescope (LAT) instrument and evidence for lensing was obtained ...
    • HESS and Suzaku observations of the Vela X pulsar wind nebula 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Ndiyavala, H.; Schutte, H.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Zywucka, N.; H.E.S.S. Collaboration (EDP Sciences, 2019)
      Context. Pulsar wind nebulae (PWNe) represent the most prominent population of Galactic very-high-energy gamma-ray sources and are thought to be an efficient source of leptonic cosmic rays. Vela X is a nearby middle-aged ...
    • Measurement of the EBL spectral energy distribution using the VHE γ-ray spectra of H.E.S.S. blazars 

      Abdalla, H.; Barnard, M.; Böttcher, M.; Davids, I.D.; Garrigoux, T.; Ivascenko, A.; Krüger, P.P.; Pekeur, N.W.; Richter, S.; Seyffert, A.S.; Spanier, F.; Sushch, I.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; H.E.S.S. Collaboration (EDP Sciences, 2017)
      Very high-energy γ rays (VHE, E ≳ 100 GeV) propagating over cosmological distances can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. The transparency ...
    • Particle transport within the pulsar wind nebula HESS J1825–137 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Ndiyavala, H.; Schutte, H.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; H.E.S.S. Collaboration (EDP Sciences, 2019)
      Context. We present a detailed view of the pulsar wind nebula (PWN) HESS J1825–137. We aim to constrain the mechanisms dominating the particle transport within the nebula, accounting for its anomalously large size and ...
    • Probing the magnetic field in the GW170817 outflow using HESS observations 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Kreter, M.; Ndiyavala, H.; Schutte, H.M.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Żywucka, N.; H.E.S.S. Collaboration (IOP Publishing, 2020)
      The detection of the first electromagnetic counterpart to the binary neutron star (BNS) merger remnant GW170817 established the connection between short γ-ray bursts and BNS mergers. It also confirmed the forging of heavy ...
    • Resolving acceleration to very high energies along the jet of Centaurus A 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Ndiyavala, H.; Schutte, H.M.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Żywucka, N.; H.E.S.S. Collaboration (Springer Nature, 2020)
      The nearby radio galaxy Centaurus A belongs to a class of active galaxies that are luminous at radio wavelengths. Most show collimated relativistic outflows known as jets, which extend over hundreds of thousands of parsecs ...
    • Resolving the Crab pulsar wind nebula at teraelectronvolt energies 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Ndiyavala, H.; Schutte, H.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; H.E.S.S. Collaboration (Nature, 2020)
      The Crab nebula is one of the most-studied cosmic particle accelerators, shining brightly across the entire electromagnetic spectrum up to very-high-energy gamma rays1,2. It is known from observations in the radio to ...
    • Search for dark matter signals towards a selection of recently detected DES dwarf galaxy satellites of the Milky Way with HESS 

      Abdallah, H.; Arcara, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Kreter, M.; Ndiyavala, H.; Schutte, H.M.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Żywucka, N.; H.E.S.S. Collaboration (APS, 2020)
      Dwarf spheroidal galaxy satellites of the Milky Way are prime targets for indirect detection of dark matter with gamma rays due to their proximity, high dark matter content, and absence of nonthermal emission processes. ...
    • Simultaneous observations of the blazar PKS 2155-304 from ultra-violet to TeV energies 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Kreter, M.; Ndiyavala, H.; Schutte, H.M.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Zywucka, N.; H.E.S.S. Collaboration; Fermi LAT (EDP Sciences, 2020)
      Here we report the results of the first ever contemporaneous multi-wavelength observation campaign on the BL Lac object PKS 2155−304 involving Swift, NuSTAR, Fermi-LAT, and H.E.S.S. The use of these instruments allows us ...
    • TeV gamma-ray observations of the binary neutron star merger GW170817 with H.E.S.S. 

      Abdalla, H.; Barnard, M.; Böttcher, M.; Garrigoux, T.; Ivascenko, A.; Krüger, P.P.; Ndiyavala, H.; Pekeur, N.W.; Seyffert, A.S.; Spanier, F.; Sushch, I.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; H.E.S.S. Collaboration (IOP Publishing, 2017)
      We search for high-energy gamma-ray emission from the binary neutron star merger GW170817 with the H.E.S.S. Imaging Air Cherenkov Telescopes. The observations presented here have been obtained starting only 5.3 hr ...
    • Upper limits on very-high-energy gamma-ray emission from core-collapse supernovae observed with H.E.S.S. 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Ndiyavala, H.; Schutte, H.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Zywucka, N.; H.E.S.S. Collaboration (EDP Sciences, 2019)
      Young core-collapse supernovae with dense-wind progenitors may be able to accelerate cosmic-ray hadrons beyond the knee of the cosmic-ray spectrum, and this may result in measurable gamma-ray emission. We searched for ...
    • Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Kreter, M.; Ndiyavala, H.; Schutte, H.M.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Żywucka, N.; H.E.S.S. Collaboration (Oxford Univ Press, 2020)
      We report on the detection of very high energy (VHE; E > 100 GeV) γ-ray emission from the BL Lac objects KUV 00311−1938 and PKS 1440−389 with the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. observations were ...
    • A very-high-energy component deep in the γ-ray burst afterglow 

      Abdalla, H.; Arcaro, C.; Backes, M.; Barnard, M.; Böttcher, M.; Chand, T.; Chandra, S.; Kreter, M.; Ndiyavala, H.; Schutte, H.M.; Seyffert, A.S.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z.; Zacharias, M.; Zywucka, N. (Nature, 2019)
      Gamma-ray bursts (GRBs) are brief flashes of γ-rays and are considered to be the most energetic explosive phenomena in the Universe1. The emission from GRBs comprises a short (typically tens of seconds) and bright prompt ...