Author(s): Aharonian F., Bazer-Bachi A.R., Becherini Y., Boisson C., Borrel V., Brion E., Brun P., Boutelier T., Charbonnier A., Chounet L.-M., Coignet G., Degrange B., Djannati-Ataï A., Dubois F., Dubus G., Espigat P., Farnier C., Feinstein F., Fiasson A., Fontaine G., Gallant Y., Gérard L., Giebels B., Glicenstein J.F., Goret P., Henri G., Jacholkowska A., Khélifi B., Marcowith A., Vasileiadis G.
(Article) Published:
The Astrophysical Journal / The Astrophysical Journal Letters, vol. 695 p.L40-L44 (2009)
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Ref HAL: in2p3-00367126_v1
Ref Arxiv: 0903.1582
DOI: 10.1088/0004-637X/695/1/L40
Ref. & Cit.: NASA ADS
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163 citations
Abstract:
We report the discovery of faint very high energy (VHE, E>100 GeV) gamma-ray emission from the radio galaxy Centaurus A in observations performed with the H.E.S.S. experiment, an imaging atmospheric Cherenkov telescope array consisting of four telescopes located in Namibia. Centaurus A has been observed for more than 120 h. A signal with a statistical significance of 5.0 sigma is detected from the region including the radio core and the inner kpc jets. The integral flux above an energy threshold of ~250 GeV is measured to be ~0.8 % of the flux of the Crab Nebula (apparent luminosity: L(>250 GeV)~2.6x10^39 erg s^-1, adopting a distance of 3.8 Mpc. The spectrum can be described by a power law with a photon index of 2.7 +/- 0.5_stat +/- 0.2_sys. No significant flux variability is detected in the data set. However, the low flux only allows detection of variability on the timescale of days to flux increments above a factor of ~15-20 (3 sigma and 4 sigma, respectively). The discovery of VHE gamma-ray emission from Centaurus A reveals particle acceleration in the source to >TeV energies and, together with M 87, establishes radio galaxies as a class of VHE emitters.
Comments: 5 pages, 4 figures, accepted for publication in ApJ Letters