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H.E.S.S. discovery of very high energy γ-ray emission from PKS 0625−354

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Abdalla, H.
Barnard, M.
Davids, I.D.
Garrigoux, T.
Ivascenko, A.
Pekeur, N.W.
Seyffert, A.S.
Spanier, F.
Sushch, I.
Van der Walt, D.J.

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Oxford Univ Press

Abstract

PKS 0625−354 (z = 0.055) was observed with the four High Energy Stereoscopic System (H.E.S.S.) telescopes in 2012 during 5.5 h. The source was detected above an energy threshold of 200 GeV at a significance level of 6.1σ. No significant variability is found in these observations. The source is well described with a power-law spectrum with photon index Γ = 2.84 ± 0.50stat ± 0.10syst and normalization (at E0 = 1.0 TeV) N0(E0) = (0.58 ± 0.22stat ± 0.12syst) × 10−12 TeV−1 cm−2 s−1. Multiwavelength data collected with Fermi-LAT, Swift-XRT, Swift-UVOT, ATOM and WISE are also analysed. Significant variability is observed only in the Fermi-LAT γ-ray and Swift-XRT X-ray energy bands. Having a good multiwavelength coverage from radio to very high energy, we performed a broad-band modelling from two types of emission scenarios. The results from a one zone lepto-hadronic and a multizone leptonic models are compared and discussed. On the grounds of energetics, our analysis favours a leptonic multizone model. Models associated to the X-ray variability constraint support previous results, suggesting a BL Lac nature of PKS 0625−354 with, however, a large-scale jet structure typical of a radio galaxy

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Abdalla, H. et al. 2018. H.E.S.S. discovery of very high energy γ-ray emission from PKS 0625−354. Monthly notices of the Royal Astronomical Society, 476(3):4187-4198. [https://doi.org/10.1093/mnras/sty439]

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