20 August 2009 Imaging and burst location with the EXIST high-energy telescope
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Abstract
The primary instrument of the proposed EXIST mission is a coded mask high energy telescope (the HET), that must have a wide field of view and extremely good sensitivity. In order to achieve the performance goals it will be crucial to minimize systematic errors so that even for very long total integration times the imaging performance is close to the statistical photon limit. There is also a requirement to be able to reconstruct images on-board in near real time in order to detect and localize gamma-ray bursts, as is currently being done by the BAT instrument on Swift. However for EXIST this must be done while the spacecraft is continuously scanning the sky. The scanning provides all-sky coverage and is also a key part of the strategy to reduce systematic errors. The on-board computational problem is made even more challenging for EXIST by the very large number of detector pixels (more than 107, compared with 32768 for BAT). The EXIST HET Imaging Technical Working Group has investigated and compared numerous alternative designs for the HET. The selected baseline concept meets all of the scientific requirements, while being compatible with spacecraft and launch constraints and with those imposed by the infra-red and soft X-ray telescopes that constitute the other key parts of the payload. The approach adopted depends on a unique coded mask with two spatial scales. Coarse elements in the mask are effective over the entire energy band of the instrument and are used to initially locate gamma-ray bursts. A finer mask component provides the good angular resolution needed to refine the burst position and reduces the cosmic X-ray background; it is optimized for operation at low energies and becomes transparent in the upper part of the energy band where an open fraction of 50% is optimal. Monte Carlo simulations and analytic analysis techniques have been used to demonstrate the capabilities of the proposed design and of the two-step burst localization procedure.
© (2009) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Gerald K. Skinner, Gerald K. Skinner, Scott Barthelmy, Scott Barthelmy, Mark H. Finger, Mark H. Finger, Jae Sub Hong, Jae Sub Hong, Garrett Jernigan, Garrett Jernigan, Steven J. Sturner, Steven J. Sturner, Branden T. Allen, Branden T. Allen, Jonathan E. Grindlay, Jonathan E. Grindlay, } "Imaging and burst location with the EXIST high-energy telescope", Proc. SPIE 7435, UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XVI, 74350B (20 August 2009); doi: 10.1117/12.830184; https://doi.org/10.1117/12.830184
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