The process of data formation for the Spectrometer/Telescope for Imaging X-rays (STIX) in Solar Orbiter

TL;DR

This paper rigorously describes how STIX data formation can be interpreted as Fourier components of solar X-ray flux, enhancing image reconstruction methods for solar flare imaging.

Contribution

It provides the first rigorous Fourier analysis of STIX data formation, enabling improved Fourier-based image reconstruction algorithms.

Findings

Integrated counts are specific Fourier components (visibilities) of photon flux.

Fourier analysis assesses the reliability of visibility interpretation.

Description facilitates advanced Fourier-based imaging algorithms.

Abstract

The Spectrometer/Telescope for Imaging X-rays (STIX) is a hard X-ray imaging spectroscopy device to be mounted in the Solar Orbiter cluster with the aim of providing images and spectra of solar flaring regions at different photon energies in the range from a few keV to around 150 keV. The imaging modality of this telescope is based on the Moire pattern concept and utilizes 30 sub-collimators, each one containing a pair of co-axial grids. This paper applies Fourier analysis to provide the first rigorous description of the data formation process in STIX. Specifically, we show that, under first harmonic approximation, the integrated counts measured by STIX sub-collimators can be interpreted as specific spatial Fourier components of the incoming photon flux, named visibilities. Fourier analysis also allows the quantitative assessment of the reliability of such interpretation. The description of STIX data in terms of visibilities has a notable impact on the image reconstruction process, since it fosters the application of Fourier-based imaging algorithms.