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Volpara, A.* ; Lupoli, A.* ; Filbir, F. ; Perracchione, E.* ; Maria Massone, A.* ; Piana, M.*

RIS: Regularized imaging spectroscopy for STIX on board Solar Orbiter.

Astron. Astrophys. 694:7 (2025)
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Context. The generation of spatially resolved count spectra and of cubes of count maps at different energies via imaging spectroscopy is one of the main goals of solar hard X-ray missions based on Fourier imaging. Thus, so far, for these telescopes, this goal has been realized via the generation of either count maps that are independently reconstructed in the different energy channels or electron flux maps reconstructed via a deconvolution of the approximate forms for the bremsstrahlung cross-section. Aims. Our aim is to introduce a regularized imaging spectroscopy method (RIS), whereby the regularization implemented in the count space imposes a smoothing constraint across contiguous energy channels, without the need for computing any deconvolution of the bremsstrahlung effect. Methods. STIX records imaging data, while computing the visibilities in the spatial frequency domain. Our RIS is a sequential scheme in which part of the information coded in the image is reconstructed at a specific energy channel and transferred to the reconstruction process at a contiguous channel via a visibility interpolation computed by means of variably scaled kernels (VSKs). Results. In the case of STIX visibilities recorded during the November 11, 2022 flaring event, we show that RIS is able to generate hard X-ray maps, whose morphology is seen to smoothly evolve from one energy channel to the contiguous one; accordingly, from these maps, it is possible to infer spatially resolved count spectra characterized by a notable numerical stability. We also show that the performance of this approach is robust with respect to both the image reconstruction method and the count energy channel utilized to trigger the sequential process. Conclusions. We conclude that RIS is not only an appropriate, but also an effective and necessary approach to constructing image cubes from STIX visibilities that are characterized by smooth behavior across count energies. Thus, it allows for the generation of numerically stable (and, thus, physically reliable) local count spectra.
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Publication type Article: Journal article
Document type Scientific Article
Corresponding Author
Keywords Gamma Rays ; Methods: Data Analysis ; Sun: Flares ; Sun: X-rays ; Techniques: Imaging Spectroscopy ; Telescopes; Rhessi; Interpolation; Flares
ISSN (print) / ISBN 0004-6361
e-ISSN 1432-0746
Journal Astronomy and Astrophysics
Quellenangaben Volume: 694, Issue: , Pages: , Article Number: 7 Supplement: ,
Publisher EDP Sciences
Publishing Place 17, Ave Du Hoggar, Pa Courtaboeuf, Bp 112, F-91944 Les Ulis Cedex A, France
Non-patent literature Publications
Reviewing status Peer reviewed
Institute(s) Institute of Biological and Medical Imaging (IBMI)
Grants Fondazione Compagnia di San Paolo
Italian Ministry of Ministry of University and Research (MUR)
Italian Ministry of University - European Union
National Recovery and Resilience Plan (NRRP)
HORIZON Europe ARCAFF Project