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Discovery of variable VHE gamma-ray emission from the binary system 1FGL J1018.6-5856
Universität Hamburg, Germany .
Max-Planck-Institut für Kernphysik, Germany ; Dublin Institute for Advanced Studies, Ireland ; National Academy of Sciences of the Republic of Armenia, Armenia .
Max-Planck-Institut für Kernphysik, Germany .
National Academy of Sciences of the Republic of Armenia, Armenia ; Yerevan Physics Institute, Armenia.
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2015 (English)In: Astronomy and Astrophysics Supplement Series, ISSN 0365-0138, E-ISSN 1286-4846, Vol. 577, article id A131Article in journal (Refereed) Published
Abstract [en]

Re-observations with the HESS telescope array of the very high-energy (VHE) source HESS J1018-589 A that is 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 (χ$^2$/ν 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 VHE binary system. The spectrum of HESS J1018-589 A is best fit with a power-law function with photon index Γ = 2.20 \plusmn 0.14$_stat$ \plusmn 0.2$_sys$. Emission is detected up to ~20 TeV. The mean differential flux level is (2.9 \plusmn 0.4) \times 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 light curve. When folded on the orbital period of 16.58 days, the rebinned light curve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the HESS phaseogram to a constant flux provides evidence of periodicity at the level of N$_sigma$\gt 3σ. The shape of the VHE phaseogram and measured spectrum suggest a low-inclination, low-eccentricity system with amodest impact from VHE γ-ray absorption due to pair production (τ \lsim 1 at 300 GeV).

Place, publisher, year, edition, pages
2015. Vol. 577, article id A131
Keywords [en]
gamma rays, stars, individual, 1FGL J1018.6-5856, radiation mechanisms, non-thermal, acceleration of particles, X-rays, binaries
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
URN: urn:nbn:se:lnu:diva-44648DOI: 10.1051/0004-6361/201525699ISI: 000357345900083Scopus ID: 2-s2.0-84930508059OAI: oai:DiVA.org:lnu-44648DiVA, id: diva2:822572
Available from: 2015-06-16 Created: 2015-06-16 Last updated: 2017-12-04Bibliographically approved

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Becherini, YvonneProkoph, HeikePunch, Michael

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