Issue |
A&A
Volume 668, December 2022
|
|
---|---|---|
Article Number | A145 | |
Number of page(s) | 12 | |
Section | The Sun and the Heliosphere | |
DOI | https://doi.org/10.1051/0004-6361/202243907 | |
Published online | 15 December 2022 |
Forward fitting STIX visibilities
1
MIDA, Dipartimento di Matematica, Università degli Studi di Genova, Via Dodecaneso 35, 16146 Genova, Italy
e-mail: volpara@dima.unige.it, massone@dima.unige.it, piana@dima.unige.it
2
Department of Physics & Astronomy, Western Kentucky University, 1906 College Heights Blvd., Bowling Green, KY 42101, USA
3
Dipartimento di Scienze Matematiche “Giuseppe Luigi Lagrange”, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 Torino, Italy
4
CNR-SPIN, Via Dodecaneso 33, 16146 Genova, Italy
5
University of Applied Sciences and Arts Northwestern Switzerland, Bahnhofstrasse 6, 5210 Windisch, Switzerland
6
ETH Zürich, Rämistrasse 101, 8092 Zürich, Switzerland
7
Space Sciences Laboratory, University of California, 7 Gauss Way, 94720 Berkeley, USA
8
INAF – OATo, Strada Osservatorio 20, 10025 Pino Torinese, Torino, Italy
Received:
29
April
2022
Accepted:
17
October
2022
Aims. We seek to determine to what extent the problem of forward fitting visibilities measured by the Spectrometer/Telescope Imaging X-rays (STIX) on board Solar Orbiter becomes more challenging with respect to the same problem in the case of previous hard X-ray solar imaging missions. In addition, we aim to identify an effective optimization scheme for parametric imaging for STIX.
Methods. This paper introduces a global search optimization for forward-fitting STIX visibilities and compares its effectiveness with respect to the standard simplex-based optimization used so far for the analysis of visibilities measured by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We made this comparison by considering experimental visibilities measured by both RHESSI and STIX, as weel as synthetic visibilities generated by accounting for the STIX signal formation model.
Results. We found that among the three global search algorithms for parametric imaging, particle swarm optimization (PSO) exhibits the best performances in terms of both stability and computational effectiveness. This method is as reliable as the simplex method in the case of RHESSI visibilities. However, PSO is significantly more robust when applied to STIX simulated and experimental visibilities.
Conclusions. A standard optimization based on local search of minima is not effective enough for forward-fitting the few visibilities sampled by STIX in the spatial frequency plane. Therefore, more sophisticated optimization schemes based on global search must be introduced for parametric imaging in the case of the Solar Orbiter X-ray telescope. The forward-fitting routine based on PSO proved to be significantly robust and reliable, and it could be considered as an effective candidate tool for parametric imaging in the STIX context.
Key words: Sun: flares / Sun: X-rays, gamma rays / techniques: image processing / telescopes
© The Authors 2022
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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