<title>Balloon-borne coded aperture telescope for arc-minute angular resolution at hard x-ray energies</title>

Abstract

We are working on the development of a new balloon-borne telescope, MARGIE (Minute-of-Arc Resolution Gamma ray Imaging Experiment). It will be a coded aperture telescope designed to image hard X-rays (in various configurations) over the 20-600 keV range with an angular resolution approaching one arc minute. MARGIE will use one (or both) of two different detection plane technologies, each of which is capable of providing event locations with sub-mm accuracies. One such technology involves the use of Cadmium Zinc Telluride (CZT) strip detectors. We have successfully completed a series of laboratory measurements using a prototype CZT detector with 375 micron pitch. Spatial location accuracies of better than 375 microns have been demonstrated. A second type of detection plane would be based on CsI microfiber arrays coupled to a large area silicon CCD readout array. This approach would provide spatial resolutions comparable to that of the CZT prototype. In one possible configuration, the coded mask would be 0.5 mm thick tungsten, with 0.5 mm pixels at a distance of 1.5 m from the central detector, giving an angular resolution of 1 arc-minute and a fully coded field of view of 12 degrees. We review the capabilities of the MARGIE telescope and report on the status of our development efforts and our plans fora first balloon flight.

<title>Three-dimensional imaging and detection efficiency performance of orthogonal coplanar CZT strip detectors</title>

“…An image plane fabricated using closely-packed arrays of CZT detector modules is a candidate for the central detector of several proposed hard X-ray (30-600 keV) coded aperture telescopes, including HEXIS (High-Energy X-ray Imaging Spectrometer), 3 AXGAM (All-sky X-ray an Gamma-ray Astronomy Monitor), 4 EXIST (Energetic X-Ray Imaging Survey Telescope), 5 and MARGIE (the Minute-of-Arc Resolution Gamma-ray Imaging Experiment). 6,7 In order to achieve angular resolutions on the order of one arc-minute (the design goal of the MARGIE program, for example), the detectors for the image plane will require sub-millimeter position resolution in three dimensions. Energy resolutions of better than 10% FWHM at 60 keV are desired for these applications.…”

CASTER: a concept for a Black Hole Finder Probe based on the use of new scintillator technologies

“…This pixel crosstalk effect can seriously degrade the imaging performance. It can be minimized at a given energy by limiting the FoV (the photon incidence angle) or the detector thickness 25 or by measuring the depth of the interaction site within the detection plane. Depth information can be used in constructing the image from different layers within the detector.…”

“…We have developed and tested the procedures for producing large coded aperture tungsten masks using relatively straightforward photolithographic etching techniques. 25 A mask pattern is produced which provides for the edge allowances required to produce the proper shaped holes. The mask pattern is transferred from CAD to a silver-based mylar acetate film using a high resolution (16,000 dpi) laser printer.…”

CASTER: a scintillator-based black hole finder probe

“…It can be minimized at a given energy by limiting the FoV (the photon incidence angle) or the detector thickness. 32 An effective way to ameliorate these limitations is to measure the depth of the interaction site within the detection plane. This permits the differentiation of "deep" interactions (where the measured position may be displaced from the entrance point) from "shallow" interactions near the top of the detector (where the crosstalk is small and the measured interaction point is a good measure of the actual entrance location).…”

“…For example, we have previously developed and tested the procedures for producing large coded aperture tungsten masks using straightforward photolithographic etching techniques. 32,34 We must also investigate the various options for the grading material(s) and thicknesses. 35 We will identify candidate approaches to mask design and fabrication and will incorporate them into instrument simulation and mission cost trade studies.…”