Very high energy gamma ray astronomy and non pulsating low mass X-ray binaries
This thesis is concerned with non pulsating Low Mass X-Ray Binaries as Very High Energy γ-ray sources, in particular Scorpius X-1; the brightest of these objects in X-rays, and the most likely to be detectable at energies above 250 GeV. After a first introductory chapter, experimental techniques presently used in Very High Energy γ-ray Astronomy are reviewed. In the third chapter statistical techniques used to quantify count rate excesses and orbital modulations are described and applied to data from Scorpius X-1. Data taken in 1988 and 1989 showing a 3cr count excess, reported previously elsewhere, are found to show orbital modulation at the 3% statistical level. The analysis of data taken on 1990 shows no signal. Periodicity tests, in particular the Rayleigh test, are also described. The principles of a segmented fast algorithm for period searches in Cerenkov data using memory limited, but relatively fast, micro-computers are shown in the fourth chapter. Various of these machines can be used simultaneously in order to achieve a large efficiency. A method to perform various trials per independent frequency is also presented. The results of period searches in data from three selected objects (Scorpius X-1, GX 5-1 and Supernova 1987A) are presented. No periodicity is found at significant level in these data. The complete power spectrum of four segments of data from Cygnus X-3 showing a signal near to 12.59 ms are also shown. The final chapter considers theoretical models developed previously for more massive systems accounting for the different physical scenario of these low mass systems. The process of pair production between high energy photons and the radiation field of the accretion disc appears as the tightest constraint on how close to the neutron star high energy photons can be produced.