Discovery of very high energy γ-ray emission from the BL Lacertae object H 2356-309 with the HESS Cherenkov telescopes
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Date
2006
Authors
Aharonian, F.
Akhperjanian, A.
Bazer-Bachi, A.
Beilicke, M.
Benbow, W.
Berge, D.
Bernlohr, K.
Boisson, C.
Bolz, O.
Borrel, V.
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Astronomy and Astrophysics (A & A), 2006; 455(2):461-466
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F. Aharonian ... G. Rowell ...and M.Ward [et al]
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Abstract
The extreme synchrotron BL Lac object H 2356-309, located at a redshift of z = 0.165, was observed from June to December 2004 with a total exposure of ≈40 h live-time with the HESS (High Energy Stereoscopic System) array of atmospheric-Cherenkov telescopes (ACTs). Analysis of this data set yields, for the first time, a strong excess of 453 γ-rays (10 standard deviations above background) from H 2356-309, corresponding to an observed integral flux above 200 GeV of I(>200 GeV) = (4.1 ±0.5) × 10 <sup>-12</sup> cm <sup>-2</sup> s <sup>-1</sup> (statistical error only). The differential energy spectrum of the source between 200 GeV and 1.3TeV is well-described by a power law with a normalisation (at 1 TeV) of N <inf>0</inf> = (3.00 ±0.80 <inf>stat</inf> ± 0.31 <inf>sys</inf>)× 10 <sup>-13</sup> cm <sup>-2</sup> s <sup>-1</sup>TeV <sup>-1</sup> and a photon index of Γ = 3.09 ± 0.24 <inf>stat</inf> ± 0.10 <inf>sys</inf>. H 2356-309 is one of the most distant BL Lac objects detected at very-high-energy γ-rays so far. Results from simultaneous observations from ROTSE-III (optical), RXTE (X-rays) and NRT (radio) are also included and used together with the HESS data to constrain a single-zone homogeneous synchrotron self-Compton (SSC) model. This model provides an adequate fit to the HESS data when using a reasonable set of model parameters. © ESO 2006.
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© The European Southern Observatory 2006