STIX X-ray microflare observations during the Solar Orbiter commissioning phase

Autor: Andrea Francesco Battaglia, Jonas Saqri, Paolo Massa, Emma Perracchione, Ewan C. M. Dickson, Hualin Xiao, Astrid M. Veronig, Alexander Warmuth, Marina Battaglia, Gordon J. Hurford, Aline Meuris, Olivier Limousin, László Etesi, Shane A. Maloney, Richard A. Schwartz, Matej Kuhar, Frederic Schuller, Valliappan Senthamizh Pavai, Sophie Musset, Daniel F. Ryan, Lucia Kleint, Michele Piana, Anna Maria Massone, Federico Benvenuto, Janusz Sylwester, Michalina Litwicka, Marek Stȩślicki, Tomasz Mrozek, Nicole Vilmer, František Fárník, Jana Kašparová, Gottfried Mann, Peter T. Gallagher, Brian R. Dennis, André Csillaghy, Arnold O. Benz, Säm Krucker
Přispěvatelé: University of Applied Sciences and Arts of Western Switzerland (HES-SO), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich] (ETH Zürich), Institute of Physics [Graz], Karl-Franzens-Universität Graz, Dipartimento di Matematica [Genova], Università degli studi di Genova = University of Genoa (UniGe), Leibniz-Institut für Astrophysik Potsdam (AIP), Univ Paris Diderot, CEA, CNRS, Lab AIM, Gif Sur Yvette, France, Trinity College Dublin, Dublin Institute for Advanced Studies (DIAS), American University Washington D.C. (AU), NASA Goddard Space Flight Center (GSFC), SUPA School of Physics and Astronomy [Glasgow], University of Glasgow, Centre Universitaire d'Informatique (CUI), Université de Genève = University of Geneva (UNIGE), Space Research Centre of Polish Academy of Sciences (CBK), Polska Akademia Nauk = Polish Academy of Sciences (PAN), Astronomical Institute [Wroclaw], University of Wrocław [Poland] (UWr), Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Astronomical Institute of the Czech Academy of Sciences (ASU / CAS), Czech Academy of Sciences [Prague] (CAS), Space Sciences Laboratory [Berkeley] (SSL), University of California [Berkeley] (UC Berkeley), University of California (UC)-University of California (UC)
Jazyk: angličtina
Rok vydání: 2021
Předmět:
Zdroj: Astronomy and Astrophysics-A&A
Astronomy and Astrophysics-A&A, 2021, 656, pp.A4. ⟨10.1051/0004-6361/202140524⟩
ISSN: 0004-6361
Popis: The Spectrometer/Telescope for Imaging X-rays (STIX) is the HXR instrument onboard Solar Orbiter designed to observe solar flares over a broad range of flare sizes, between 4-150 keV. We report the first STIX observations of microflares recorded during the instrument commissioning phase in order to investigate the STIX performance at its detection limit. This first result paper focuses on the temporal and spectral evolution of STIX microflares occuring in the AR12765 in June 2020, and compares the STIX measurements with GOES/XRS, SDO/AIA, and Hinode/XRT. For the observed microflares of the GOES A and B class, the STIX peak time at lowest energies is located in the impulsive phase of the flares, well before the GOES peak time. Such a behavior can either be explained by the higher sensitivity of STIX to higher temperatures compared to GOES, or due to the existence of a nonthermal component reaching down to low energies. The interpretation is inconclusive due to limited counting statistics for all but the largest flare in our sample. For this largest flare, the low-energy peak time is clearly due to thermal emission, and the nonthermal component seen at higher energies occurs even earlier. This suggests that the classic thermal explanation might also be favored for the majority of the smaller flares. In combination with EUV and SXR observations, STIX corroborates earlier findings that an isothermal assumption is of limited validity. Future diagnostic efforts should focus on multi-wavelength studies to derive differential emission measure distributions over a wide range of temperatures to accurately describe the energetics of solar flares. Commissioning observations confirm that STIX is working as designed. As a rule of thumb, STIX detects flares as small as the GOES A class. For flares above the GOES B class, detailed spectral and imaging analyses can be performed.
Comment: 19 pages, 11 figures
Databáze: OpenAIRE
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