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- Title
Discovery of variable VHE γ-ray emission from the binary system 1FGL J1018.6-5856.
- Authors
Abramowski, A.; Aharonian, F.; Benkhali, F. Ait; Akhperjanian, A. G.; Angüner, E. O.; Backes, M.; Balzer, A.; Becherini, Y.; Tjus, J. Becker; Berge, D.; Bernhard, S.; Bernlöhr, K.; Birsin, E.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bordas, P.; Bregeon, J.; Brun, F.
- Abstract
Re-observations with the H.E.S.S. telescope array of the very-high-energy (VHE) source HESS J1018-589 A coincident with the Fermi-LAT γ-ray binary 1FGL J1018.6-5856 have resulted in a source detection significance of more than 9σ, and the detection of variability (χ2/v of 238.3/155) in the emitted γ-ray flux. This variability confirms the association of HESS J1018-589 A with the high-energy γ-ray binary detected by Fermi-LAT, and also confirms the point-like source as a new very-high-energy binary system. The spectrum of HESS J1018-589 A is best fit with a power-law function with photon index Γ=2.20±0.14stat±0.2sys. Emission is detected up to ~20 TeV. The mean differential flux level is (2.9±0.4)×10-13 TeV-1 cm-2 s-1 at 1 TeV, equivalent to ~1% of the flux from the Crab Nebula at the same energy. Variability is clearly detected in the night-by-night lightcurve. When folded on the orbital period of 16.58 days, the rebinned lightcurve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the H.E.S.S. phaseogram to a constant flux provides evidence of periodicity at the level of 3σ. The shape of the VHE phaseogram and measured spectrum suggest a low inclination, low eccentricity system with a modest impact from VHE γ-ray absorption due to pair production (τ ≲1 at 300 GeV).
- Subjects
BINARY systems (Astronomy); GAMMA ray telescopes; STELLAR radiation; CRAB Nebula; BINARY stars
- Publication
Astronomy & Astrophysics / Astronomie et Astrophysique, 2015, Vol 577, p1
- ISSN
0004-6361
- Publication type
Article
- DOI
10.1051/0004-6361/201525699