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Etude des propriétés spectrales et de la variabilité de l'emission gamma supérieure à 250 GeV des noyaux actifs de galaxies de type blazar observés dans le cadre de l'expérience C.A.T.

Abstract : After briefly recalling the physics addressed by very high-energy y-ray astronomy, the C.A.T. ("Cerenkov Array at Thémis") imaging telescope is presented, with emphasis on recent calibration results, which is an important aspect of atmospheric Cherenkov detectors: no direct calibration is possible, and an understanding of the telescope requires a continual comparison of the results derived from numerical calculations with real data, including in particular those taken on the Crab nebula (standard candle). The ^y-ray signalextraction procedure and the spectral reconstruction method are explained in detail, checked, and validated this way. Then, the results obtained for the blazars Markarian 501 and Markarian 421 are given: correlation between X-ray (> keV) and TeV gamma-ray emissions is proven for both sources; rapid TeV variability is observed, sometimes within a few hours in the case of Markarian 421; Markarian 501 appears, however, more extreme: its maximum power output lies around 500 GeV, and a spectral hardening is observed for the most flaring periods. These results support the recent spectral sequence proposed for the blazar class unification; they suggest a very compact emission zone (N10-3 parsec), propagating with relativistic motion at the base of the radio jets of these objects, and containing a unique population of electrons responsible for the non-thermal multi-wavelength observed emission. A Synchrotron Self-Compton model is succesfully applied to the data taken on Markarian 501 in April 1997. Finally, the search for a gamma-ray signal from 20 other blazars is presented, and an upper limit to their TeV emission is established.
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https://tel.archives-ouvertes.fr/tel-00002448
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Submitted on : Friday, February 21, 2003 - 3:40:53 PM
Last modification on : Wednesday, December 9, 2020 - 3:13:12 PM
Long-term archiving on: : Friday, April 2, 2010 - 6:54:31 PM

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  • HAL Id : tel-00002448, version 1

Citation

Frédéric Piron. Etude des propriétés spectrales et de la variabilité de l'emission gamma supérieure à 250 GeV des noyaux actifs de galaxies de type blazar observés dans le cadre de l'expérience C.A.T.. Cosmologie et astrophysique extra-galactique [astro-ph.CO]. Université Paris Sud - Paris XI, 2000. Français. ⟨tel-00002448⟩

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