Observation of solar energetic particles with Metis on board Solar Orbiter on February 25, 2023

¹ DiSPeA, University of Urbino Carlo Bo, Urbino, PU, Italy
e-mail: catia.grimani@uniurb.it
² INFN, Florence, Italy
³ European Space Agency, ESAC, Camino Bajo del Castillo s/n, Villafranca del Castillo, 28692 Villanueva de la Cañada, Madrid, Spain
⁴ Politecnico di Milano, Milano, Italy
⁵ INAF-Astrophysical Observatory of Torino, Torino, Italy
⁶ Institut für Experimentelle und Angewandte Physik, Christan-Albrechts-Universität zu Kiel, Kiel, Germany
⁷ Universidad de Alcalá, Space Research Group, 28805 Alcalá de Henares, Spain
⁸ INAF – Astronomical Observatory of Capodimonte, Naples, Italy
⁹ CNR-IFN, Via Trasea 7, 35131 Padova, Italy
¹⁰ CISAS, Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”, via Venezia 15, 35131 Padova, Italy
¹¹ Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Ringlaan -3- Av. Circulaire, 1180 Brussels, Belgium
¹² INAF – Astrophysical Observatory of Trieste, Trieste, Italy
¹³ Dip. di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Via G. Marzolo 8, 35131 Padova, Italy
¹⁴ ASI – Italian Space Agency, Via del Politecnico snc, 00133 Rome, Italy
¹⁵ University of Florence, Physics and Astronomy Department, Largo E. Fermi 2, 50125 Florence, Italy
¹⁶ INAF – Arcetri Astrophysical Observatory, Largo Enrico Fermi 5, 50125 Florence, Italy
¹⁷ INAF-Astrophysical Observatory of Catania, Catania, Italy
¹⁸ MPS, Göttingen, Germany
¹⁹ INAF – Institute for Space Astrophysics and Cosmic Physics, Milan, Italy

Received: 29 January 2024
Accepted: 2 March 2024

Abstract

Context. The Solar Orbiter Metis coronagraph captures images of the solar corona in both visible (VL) and ultraviolet (UV) light. Tracks ascribable to the passage of galactic and solar particles appear in the Metis images. An algorithm implemented in the Metis processing electronics allows us to separate the pixels fired by VL photons from those crossed by high-energy particles. These spurious pixels are stored in cosmic-ray matrices that can be visually analyzed for particle monitoring deep into the spacecraft’s interior. This algorithm has been enabled for the VL instrument only, since the process of separating the particle tracks from pixels fired by photons in the UV images was shown to be quite challenging with respect to a quantitative analysis.

Aims. This work is aimed at studying galactic cosmic rays (GCRs) and solar energetic particles (SEPs) with the Metis cosmic-ray matrices in February 2023.

Methods. We compared a visual analysis of Metis cosmic-ray matrices gathered on February 22, 2023, with GCRs only, and on February 25, 2023 with both GCRs and SEPs, to Monte Carlo simulations of the VL instrument during the same days.

Results. We estimated the solar modulation parameter associated with the GCR proton energy spectrum in February 2023. We show that Metis plays the role of monitoring galactic and solar protons. The Metis particle observations are used for the diagnostics of the VL instrument performance and to study the spacecraft inner charging from solar minimum towards the next solar maximum. These achievements have been attained with the benefit of the joint observations of Metis, the Energetic Particle Detector/High Energy Telescope, and near-Earth and Earth-based instruments.