DISCOVERY OF THE HARD SPECTRUM VHE γ-RAY SOURCE HESS J1641–463
- Institut für Experimentalphysik, Universität Hamburg, Luruper Chaussee 149, D-22761 Hamburg (Germany)
- Max-Planck-Institut für Kernphysik, PO Box 103980, D-69029 Heidelberg (Germany)
- National Academy of Sciences of the Republic of Armenia, Marshall Baghramian Avenue, 24, 0019 Yerevan, Republic of Armenia (Armenia)
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany)
- Department of Physics, University of Namibia, Private Bag 13301, Windhoek (Namibia)
- Department of Physics, University of Durham, South Road, Durham DH1 3LE (United Kingdom)
- GRAPPA, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands)
- Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków (Poland)
- Department of Physics and Electrical Engineering, Linnaeus University, 351 95 Växjö (Sweden)
- Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum (Germany)
- GRAPPA, Anton Pannekoek Institute for Astronomy and Institute of High-Energy Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands)
- Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität Innsbruck, A-6020 Innsbruck (Austria)
- Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, F-91128 Palaiseau (France)
- Centre for Space Research, North-West University, Potchefstroom 2520 (South Africa)
This Letter reports the discovery of a remarkably hard spectrum source, HESS J1641–463, by the High Energy Stereoscopic System (H.E.S.S.) in the very high energy (VHE) domain. HESS J1641–463 remained unnoticed by the usual analysis techniques due to confusion with the bright nearby source HESS J1640–465. It emerged at a significance level of 8.5 standard deviations after restricting the analysis to events with energies above 4 TeV. It shows a moderate flux level of φ(E>1 TeV) = (3.64 ± 0.44{sub stat} ± 0.73{sub sys}) × 10{sup –13} cm{sup –2} s{sup –1}, corresponding to 1.8% of the Crab Nebula flux above the same energy, and a hard spectrum with a photon index of Γ = 2.07 ± 0.11{sub stat} ± 0.20{sub sys}. It is a point-like source, although an extension up to a Gaussian width of σ = 3 arcmin cannot be discounted due to uncertainties in the H.E.S.S. point-spread function. The VHE γ-ray flux of HESS J1641–463 is found to be constant over the observed period when checking time binnings from the year-by-year to the 28 minute exposure timescales. HESS J1641–463 is positionally coincident with the radio supernova remnant SNR G338.5+0.1. No X-ray candidate stands out as a clear association; however, Chandra and XMM-Newton data reveal some potential weak counterparts. Various VHE γ-ray production scenarios are discussed. If the emission from HESS J1641–463 is produced by cosmic ray protons colliding with the ambient gas, then their spectrum must extend close to 1 PeV. This object may represent a source population contributing significantly to the galactic cosmic ray flux around the knee.
- OSTI ID:
- 22364947
- Journal Information:
- Astrophysical Journal Letters, Vol. 794, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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