Low energy gamma ray astronomy

Martin, Stephen Julian (1978) Low energy gamma ray astronomy. University of Southampton, Doctoral Thesis.

Abstract

Various types of low energy gamma-ray detector and their successful observations are reviewed. A novel type of gamma-ray telescope developed by Southampton University and the Laboratorio di Fisica Cosmica, Milan in fully described together with extensive toots and calibrations. The telescope has semi-active shielding and requires a gamma-ray to interact in a liquid scintillator and subsequently in a flat crystal. The problems occuring in the use of low energy gamma-ray detectors, such as interactions due to cosmic rays, atmospheric neutrons, and atmospheric gamma-rays have been investigated with respect to the Milan-Southampton telescope, but this work may be applied to many other types of detector.The Milan-Southampton telescope, together with a passively shielded X-ray detector and an actively shielded X-ray detector were flown from the Rational Centre for Atmospheric Research Balloon Launching Site at Palestine Tea_xas in May 1977. Data analysis is presented to show how this novel type of detector functioned during flight.The Seyfert Galaxy RGC4151 was observed to have a spectrum of (1.1+0.4)x10 2E 1 photons cra 2 s 1 MeV 1 in the energy range 9.15 to 20 MeV and a positive flux was also found for CG135+1, using the Nat crystal of the Milan-Southampton telescope only. A positive flux was observed from the Crab Nebula by applying the method of bidimensional analysis to gamma ray events (~coincidence events~) depositing energy in both the liquid scintillator and Iial within a period of 200ns. The usefulness of this method is explained.

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