Discovery of Very High Energy γ-Ray Emission from Centaurus a with H.E.S.S

• Published in: Astrophysical journal. Letters 2009-04, Vol.695 (1), p.L40-L44
• Main Authors: Aharonian, F, Becherini, Y, Behera, B, Benbow, W, Boisson, C, Brucker, J, Brun, P, Bühler, R, Boutelier, T, Chaves, R. C. G, Coignet, G, Dalton, M, Daniel, M. K, Deil, C, Dickinson, H. J, Djannati-Ataï, A, Dyks, J, Dyrda, M, Emmanoulopoulos, D, Espigat, P, Farnier, C, Feinstein, F, Fiasson, A, Fontaine, G, Gallant, Y. A, Glicenstein, J.-F, Göhring, D, Hauser, D, Henri, G, Hermann, G, Hofmann, W, Horns, D, Jacholkowska, A, Katarzyński, K, Katz, U, Kaufmann, S, Kendziorra, E, Kerschhaggl, M, Khangulyan, D, Khélifi, B, Keogh, D, Kluźniak, W, Kneiske, T, Komin, Nu, Kosack, K, Lamanna, G, Lohse, T, Marandon, V, Martin, J. M, Marcowith, A, McComb, T. J. L, Moderski, R, Naumann-Godo, M, de Naurois, M, Nekrassov, D, Niemiec, J, Nolan, S. J, Ohm, S, Orford, K. J, Pedaletti, G, Pelletier, G, Petrucci, P.-O, Pühlhofer, G, Punch, M, Raue, M, Renaud, M, Rieger, F, Ripken, J, Rosier-Lees, S, Rowell, G, Rudak, B, Rulten, C. B, Ruppel, J, Sahakian, V, Schlickeiser, R, Schöck, F. M, Schwanke, U, Schwemmer, S, Shalchi, A, Sikora, M, Sol, H, Spangler, D, Stawarz, Ł, Steenkamp, R, Stegmann, C, Superina, G, Szostek, A, Terrier, R, Tluczykont, M, van Eldik, C, Venter, C, Venter, L, Vialle, J. P, Vincent, P, Vivier, M, Völk, H. J, Volpe, F, Wagner, S. J, Zdziarski, A. A, Zech, A
• Format: Article
• Language: English
• Subjects: Astroparticle Physics; Astropartikelfysik; Astrophysics; Cosmology and Extra-Galactic Astrophysics; galaxies: active; galaxies: individual (Cen A); gamma rays: observations; Physics; Sciences of the Universe
• ISSN: 1538-4357; 0004-637X; 2041-8205; 1538-4357; 2041-8213
• DOI: 10.1088/0004-637X/695/1/L40

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.