Abstract
Abstract In this work we aimed to develop the image reconstruction algorithm without any analytical simplifications and restrictions. In our method we abandon Fourier’s approach to image reconstruction, and instead use the number of counts recorded in each detector pixel, and then reconstruct each image using a classical Richardson-Lucy algorithm. Among similar works performed in the past, our approach is based, for the first time, on the real geometry of STIX. We made a preliminary analysis of expected differences in STIX imaging which may occur due to usage of slightly different geometries. The other difference is that we use single-pixel-response maps. Namely, knowing the instrument geometry we are able to calculate the detector response for point sources covering entire the solar disc. Next, we iteratively combine them with varying weights until the best match between reconstructed and observed detector responses is achieved. Preliminary tests revealed that the developed algorithm reproduces high quality images. The algorithm is moderately fast, but the result comparable to CLEAN algorithm is obtained within 20-50 iteration steps which takes less than 2 seconds on typical portable computer configuration. The location, size and intensity of reconstructed sources are very close to simulated ones. Therefore the algorithm is very well suited for the detailed photometry of the solar HXR sources. Moreover, its simplicity allows to improve photon transmission calculation in case of any grids uncertainties measured after the launch.
Highlights
The idea of HXR telescopes using Fourier techniques was given by Oda (1965)
The Spectrometer Telescope for Imaging X-rays (STIX) (Krucker et al 2020) is one of the instruments installed on board the Solar Orbiter mission (Müller et al 2013)
The photometry from images reconstructed with RL algorithm is very good. At this point we are not able to compare with PIXON algorithm as it is not implemented for STIX data yet
Summary
The idea of HXR telescopes using Fourier techniques was given by Oda (1965). The rst observation with such equipment was a rocket experiment which allowed the X-ray imaging of the Crab nebula (Oda et al 1967). The Spectrometer Telescope for Imaging X-rays (STIX) (Krucker et al 2020) is one of the instruments installed on board the Solar Orbiter mission (Müller et al 2013). It will record solar are spectra and images in the energy range 4 − 150 keV. Our algorithm uses transmission functions calculated for single sources smaller than the STIX spatial resolution, giving detector count rates. This is the most straightforwad approach to image reconstruction. We brie y describe STIX telescope (Section 2), the grid transmission (Section 3), the reconstruction algorithm (Section 4), the algorithm performance for some typical source distributions (Section 5), and discussion of results (Section 6)
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