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- Discovery of Very High Energy Gamma-Ray Emission from the BL Lac Object H2356-309 with the H.E.S.S. Cherenkov Telescopes doi link

Author(s): Aharonian F., R. Bazer-Bachi A., Boisson C., Borrel V., Chounet L.-M., Degrange B., Djannati-Ataï A., Dubus G., Espigat P., Feinstein F., Fontaine G., Gallant Y., Giebels B., F. Glicenstein J., Goret P., Henri G., Jacholkowska Agnieszka, Khélifi B., Lemière A., Lemoine-Goumard M., Marcowith A., Pelletier G., Pita S., Punch M., Saugé L., Sol H., Superina G., Terrier R., G. Théoret C., Vasileiadis G.

(Article) Published: Astronomy & Astrophysics, vol. 455 p.461-466 (2006)
Links openAccess full text : arxiv


Ref HAL: in2p3-00124806_v1
Ref Arxiv: astro-ph/0607569
DOI: 10.1051/0004-6361:20054732
Ref. & Cit.: NASA ADS
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Abstract:

The extreme synchrotron BL Lac object H2356-309, located at a redshift of z = 0.165, was observed from June to December 2004 with a total exposure of approx. 40 h live-time with the H.E.S.S. (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 gamma-rays (10 standard deviations above background) from H2356-309, corresponding to an observed integral flux above 200 GeV of I(>200GeV) = (4.1+-0.5) 10^12 cm^-2.s^-1 (statistical error only). The differential energy spectrum of the source between 200 GeV and 1.3 TeV is well-described by a power law with a normalisation (at 1 TeV) of N_0 = (3.00 +- 0.80_stat +- 0.31_sys) 10^-13 cm^-2.s^-1.TeV^-1 and a photon index of Gamma = 3.09 +- 0.24_stat +- 0.10_sys. H2356-309 is one of the most distant BL Lac objects detected at very-high-energy gamma-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 H.E.S.S. data to constrain a single-zone homogeneous synchrotron self-Compton (SSC) model. This model provides an adequate fit to the H.E.S.S. data when using a reasonable set of model parameters.



Comments: 7 pages, 4 figures, accepted for publication in Astronomy and Astrophysics (05/07/2006)