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The PMTRAS Roll Aspect System on RHESSI  

Gordon J. Hurford   Submitted: 2002-09-19 14:48

High-resolution solar hard X-ray imaging on the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft is achieved by a set of rotating modulation collimators. The interpretation of the observed time-modulated X-ray flux in terms of high-resolution, accurately located images requires continuous, arcminute roll aspect, which at present is provided by the 'Photo-Multiplier Tube Roll Aspect System' (PMTRAS). This paper describes the PMTRAS operating principles, hardware implementation, calibration, performance and data analysis approach, with emphasis on its effect on RHESSI imaging.

Authors: G. J. Hurford and D. W. Curtis
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Publication Status: Solar Physics (in press)
Last Modified: 2002-09-23 17:09
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The RHESSI Imaging Concept  

Gordon J. Hurford   Submitted: 2002-09-19 14:24

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) images solar hard X-ray and gamma-rays from 3 keV to 15 MeV with spatial resolution as high as 2.3 arcseconds. Instead of conventional optics, nine rotating modulation collimators are used to time-modulate the incident flux as the spacecraft rotates in a manner which depends on the location and morphology of the source. Starting from the arrival time of individual photons, ground-based software then uses the time-modulated signals to reconstruct the image of the source. The purpose of this paper is to convey both and intuitive feel and the mathematical basis for this imaging process along with its strengths and weaknesses. Following a review of the relevant hardware, the imaging principles and the basic back projection method are described, along with their relation to Fourier Transforms. Several specific algorithms (CLEAN, MEM. PIXONS and Forward Fitting) applicable to RHESSI imaging are briefly described.

Authors: G. J. Hurford, E. J. Schmahl, A. J. Conway, B. R. Dennis, R. A. Schwartz, R.P.Lin, J. McTiernan, D. M. Smith, C. Johns-Krull, A. Csillaghy, M. J. Aschwanden and T. R. Metcalf
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Publication Status: Solar Physics (in press)
Last Modified: 2002-09-20 11:37
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The PMTRAS Roll Aspect System on RHESSI
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