Corbin Edward Covault

Techniques For Removing Non-uniform Background In Coded-aperture Imaging On The Energetic X-ray Imaging Telescope Experiment

It is found that the subtractive flat field technique for nonuniform background illumination is generally effective at removing background systematics for stationary mask experiments such as the energetic X-ray imaging experiment. The time dependence of intensity and the two-dimensional shape of the background detector image during the flight are explored. A flat field image is constructed from observations where X-ray sources were absent from the field of view. It is shown that this technique can successfully reduce RMS fluctuations to within a few percent of ideal Poisson statistics. The quality of the flat field does not appear to be a strong function of radius and can be used effectively out to the edge of the detector to remove the strong background ring. >

Calibration and performance of the Energetic X-ray Imaging Telescope Experiment

The final integration and testing of the Energetic X-ray Imaging Telescope Experiment (EXITE) are described. The detector and telescope as finally assembled are described, and problems as well as solutions are detailed. The preflight calibration of the position-sensitive NaI detector revealed unanticipated effects in the energy spectra. In particular, an effect due to surface roughness (lack of firm optical polishing) on the crystal was found and calibrated. The radial variation of gain and resolution in the detector was also measured, and so-called flat fielding methods have been derived to analyze the data. The integration of the EXITE detector and gondola systems is described. Several novel features were developed for the EXITE gondola, most notably a shock absorber system. The performance of the detector and gondola systems was evaluated on the first balloon flight from Australia (May 1988) and a second flight from Ft. Sumner, NM (October 1988). >

Characteristics of EXITE and plans for SN 1987A

The development, integration, and testing of the Energetic X‐ray Imaging Telescope Experiment (EXITE) are described. EXITE is a balloon‐borne hard x‐ray imaging payload with high sensitivity in the 20–300 keV band, angular resolution of 22 arcmin (with source locations to ∼2 arcmin) in a 3.4° FWHM field‐of‐view and energy resolution of 9% at 122 keV. Details of the detector system, a 34 cm diameter NaI scintillation crystal with image intensification and position‐sensitive readout, are described as well as the integration and testing of EXITE into a new balloon gondola with stable (∼1 arcmin) pointing. EXITE is able to carry out high‐sensitivity (∼10 mCrab) observations of SN 1987A to measure the Compton‐degraded x‐ray and gamma ray continuum, to search for the 122 keV cobalt‐57 line, and (at 0.1 msec time resolution) to search for the new pulsar thought to have been produced in the Sn 1987A event.

Design And Performance Of A Day/night Aspect System For The EXITE Balloon-borne Hard X-ray Telescope

We report on the design, development, testing and flight usage of a complete aspect system for the balloon borne Energetic X-ray Imaging Telescope Experiment (EXITE) payload. The aspect systems are designed to provide both real-time and postfacto aspect information for the telescope pointing direction. The aspect system included two independent day-time systems: a sun sensor for determination of the solar azimuth and an integrating CCD TV camera, with deepred filter, for direct detection of bright stars in the day sky. The night-time aspect system included an intensified CCD camera and TV link for direct viewing and recording of the telescope pointing direction. All three systems were tested and used on a successful balloon flight of the EXITE payload from Alice Springs, AUS tralia, on May 9-10, 1989. Real-time aspect was obtained at the 10 arcmin level, sufficient for initial target acquisition and subsequent gyro drift updates for source tracking, for both day and night targets using the sun-semr and intensified TV systems, respectively. Postfacto aspect at the & 3 arcmin level is obtained. Analysis of the near-IR CCD images of bright star fields recorded in daytime at balloon altitudes (4 g/cm2) is in progress and will be reported in a subsequent publication.