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Contribution a la calorimetrie du telescope spatial a rayon gamma GLAST et etude des cascades eletron-photon sur le rayonnement diffus extragalactique.

Abstract : Starting September 2007, the Gamma Large Array Space Telescope (GLAST) will observe Rays of energy between 100 MeV and 300 GeV. A siliceous-strip tracker measures their direction and a calorimeter their energy. The latter is rendered hodoscopique thanks to the disposition of its CsI(Tl) crystals. Weighting 2 tons in all, these are inserted in an epoxy and carbon-ber structure for protection during take-o. Inside each crystal, tapering of the signal, coupled with double diodes at each end, allows for the measure of both the energy deposited in that crystal and the mean position of the deposit. On Earth, calibration occurs through the use of cosmic muons. Rays interact with the detector by creating electromagnetic showers. Because of constraints on the design of this space-based calorimeter, only a varying fraction of a shower's energy is deposited inside the calorimeter. This fraction depends on shower energy, direction and proximity to the detector's walls. The ray energy (E) is reconstructed trough the optimisation of an estimator as a function of these parameters. The estimator is based on the energy deposited inside the calorimeter (Q) and observables which anti-correlate with Q when E is axed, thus reducing Q's variance. The reconstruction algorithm proceeds with a maximum likelihood on this estimator. Extragalactic rays may initiate electron-photon cascades on the photon background. Observed spectra are a function of the ray attenuation, allowing in return for a measure of the infrared background, and cascade emissions. A spectral signature of the extragalactic magnetic field is considered.
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Submitted on : Thursday, July 29, 2010 - 9:06:59 AM
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Pol d'Avezac. Contribution a la calorimetrie du telescope spatial a rayon gamma GLAST et etude des cascades eletron-photon sur le rayonnement diffus extragalactique.. Physique [physics]. Ecole Polytechnique X, 2006. Français. ⟨pastel-00002297⟩

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