## Doctoral Dissertations

Spring 1987

Dissertation

Physics

#### Degree Name

Doctor of Philosophy

#### Abstract

This dissertation presents the results from a balloon-borne experiment, referred to as the Directional Gamma-Ray Telescope (DGT), which is designed to image celestial gamma-rays over the energy range 160 keV to 9.3 MeV. It utilizes a technique known as coded aperture imaging in order to obtain spatially resolved images of the sky with an angular resolution of $3.8\sp\circ.$ This detector is the first flight-ready instrument of this type operating at energies above 160 keV. The first successful balloon flight of this instrument took place on 1984 October 1-2. During the thirty hours in which the payload remained at float altitude, imaging observations of a number of sky regions were obtained, including observations of the Crab and Cygnus regions.

The Crab Nebula/pulsar was observed to have a featureless power-law spectrum with a best fit form of $5.1 \times 10\sp{-3} {\rm E\sb{MeV}}\sp{-1.88}$ photons ${\rm cm\sp{-2}\ s\sp{-1}\ MeV}\sp{-1},$ consistent with previous measurements. We have placed $3\sigma$ upper limits on previously observed line emission at energies of 400 keV and 1049 keV; the results are $3.0 \times 10\sp{-3}$ and $1.9 \times 10\sp{-3}$ photons ${\rm cm\sp{-2}\ s}\sp{-1},$ respectively. These upper limits lie below some previous measurements of this emission. We also place upper limits on the emission from the x-ray binary source A0535+26 and the anticenter diffuse emission.

Emission from Cyg X-1 was observed up to $\sim$10 MeV. At energies below 1 MeV, the data are consistent with a single-temperature inverse Compton model, with an electron temperature, ${\rm kT\sb{e}},$ of $\sim$80 keV and an optical depth, $\tau,$ of $\sim$2.0. The inverse Compton model is often employed to explain the observed x-ray emission. In the 2-9.3 MeV range, the DGT results show emission which is not readily understood in the context of the inverse Compton model. We suggest that a second component, possibly produced by some non-thermal mechanism, may be necessary to explain the observations. Finally, upper limits are also derived for the flux from Cygnus X-3.

COinS