62 articles – 637 Notices  [english version]
 HAL : in2p3-00024439, version 1
 arXiv : astro-ph/0506319
 Astronomy and Astrophysics 437 (2005) 95-99
 Observations of Mkn 421 in 2004 with H.E.S.S. at large zenith angles
 HESS Collaboration(s)
 (2005)
 Mkn 421 was observed during a high flux state for nine nights in April and May 2004 with the fully operational High Energy Stereoscopic System (H.E.S.S.) in Namibia. The observations were carried out at zenith angles of 60$^\circ$--65$^\circ$, which result in an average energy threshold of 1.5 TeV and a collection area reaching 2 km$^2$ at 10 TeV. Roughly 7000 photons from Mkn 421 were accumulated with an average gamma-ray rate of 8 photons/min. The overall significance of the detection exceeds 100 standard deviations. The light-curve of integrated fluxes above 2 TeV shows changes of the diurnal flux up to a factor of 4.3. For nights of high flux, intra-night variability is detected with a decay time of less than 1 hour. The time averaged energy spectrum is curved and is well described by a power-law with a photon index $\egamm$ and an exponential cutoff at $\ecut$ TeV and an average integral flux above 2 TeV of 3 Crab flux units. Significant variations of the spectral shape are detected with a spectral hardening as the flux increases. Contemporaneous multi-wavelength observations at lower energies (X-rays and gamma-rays above $\approx 300$ GeV) indicate smaller relative variability amplitudes than seen above 2 TeV during high flux state observed in April 2004.
 Thème(s) : Physique/Astrophysique/Cosmologie et astrophysique extra-galactiquePlanète et Univers/Astrophysique
 Mot(s)-clé(s) : galaxies: individual: Mkn 421
 Lien vers le texte intégral : http://fr.arXiv.org/abs/astro-ph/0506319
 in2p3-00024439, version 1 http://hal.in2p3.fr/in2p3-00024439 oai:hal.in2p3.fr:in2p3-00024439 Contributeur : Dominique Girod <> Soumis le : Lundi 30 Octobre 2006, 20:46:30 Dernière modification le : Lundi 30 Octobre 2006, 21:00:25