Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Andrea Francesco Battaglia
Wen Wang
Jonas Saqri
Tatiana Podladchikova
Astrid M. Veronig
Hannah Collier
Ewan C. M. Dickson
Olena Podladchikova
Christian Monstein
Alexander Warmuth
Frédéric Schuller
Louise Harra
Säm Krucker
Abstract： One of the main science questions of the Solar Orbiter and Parker Solar Probe missions deals with understanding how electrons in the lower solar corona are accelerated and how they subsequently access interplanetary space. We aim to investigate the electron acceleration and energy release sites as well as the manner in which accelerated electrons access the interplanetary space in the case of the SOL2021-02-18T18:05 event, a GOES A8 class microflare associated with a coronal jet. This study takes advantage of three different vantage points, Solar Orbiter, STEREO-A, and Earth, with observations ranging from radio to X-ray. Multi-wavelength timing analysis combined with UV/EUV imagery and X-ray spectroscopy by Solar Orbiter/STIX (Spectrometer/Telescope for Imaging X-rays) is used to investigate the origin of the observed emission during different flare phases. The event under investigation satisfies the classical picture of the onset time of the acceleration of electrons coinciding with the jet and the radio type III bursts. This microflare features prominent hard X-ray nonthermal emission down to at least 10 keV and a spectrum that is much harder than usual for a microflare with a spectral index of 2.9. From Earth's vantage point, the microflare is seen near the limb, revealing the coronal energy release site above the flare loop in EUV, which, from STIX spectroscopic analysis, turns out to be hot (at roughly the same temperature of the flare). Moreover, this region is moving toward higher altitudes over time (about 30 km/s). During the flare, the same region spatially coincides with the origin of the coronal jet. We conclude that the energy release site observed above-the-loop corresponds to the electron acceleration site, corroborating that interchange reconnection is a viable candidate for particle acceleration in the low corona on field lines open to interplanetary space.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Paolo Massa
Gordon. J. Hurford
Anna Volpara
Matej Kuhar
Andrea Francesco Battaglia
Hualin Xiao
Diego Casadei
Emma Perracchione
Sara Garbarino
Sabrina Guastavino
Hannah Collier
Ewan C. M. Dickson
Daniel F. Ryan
Shane A. Maloney
Frederic Schuller
Alexander Warmuth
Anna Maria Massone
Federico Benvenuto
Michele Piana
Säm Krucker
Abstract： Aims. To provide a schematic mathematical description of the imaging concept of the Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter. The derived model is the fundamental starting point for both the interpretation of STIX data and the description of the data calibration process. Methods. We describe the STIX indirect imaging technique which is based on spatial modulation of the X-ray photon flux by means of tungsten grids. We show that each of 30 STIX imaging sub-collimators measures a complex Fourier component of the flaring X-ray source corresponding to a specific angular frequency. We also provide details about the count distribution model, which describes the relationship between the photon flux and the measured pixel counts. Results. We define the image reconstruction problem for STIX from both visibilities and photon counts. We provide an overview of the algorithms implemented for the solution of the imaging problem, and a comparison of the results obtained with these different methods in the case of the SOL2022-03-31T18 flaring event.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Hualin Xiao
Shane Maloney
Säm Krucker
Ewan Dickson
Paolo Massa
Erica Lastufka
Andrea Francesco Battaglia
Laszlo Etesi
Nicky Hochmuth
Frederic Schuller
Daniel F. Ryan
Olivier Limousin
Hannah Collier
Alexander Warmuth
Michele Piana
Abstract： The Spectrometer/Telescope for Imaging X-rays (STIX) onboard Solar Orbiter observes solar X-ray emission in the range of 4 to 150 keV and produces spectra and images of solar flares over a wide range of flare magnitudes. During nominal operation, STIX continuously generates data. A constant data flow requires fully automated data processing pipelines to process and analyze and a data platform to manage, visualize, and distribute the data products to the scientific community. The STIX Data Center has been built to fulfill these needs. In this paper, we outline its main components to help the community better understand the tools and data it provides. Methods. The STIX Data Center is operated at the University of Applied Sciences and Arts Northwestern Switzerland (FHNW) and consists of automated processing pipelines and a data platform. The pipelines process STIX telemetry data, perform common analysis tasks and generate data products at different processing levels. They have been designed to operate fully automatically with minimal human intervention. The data platform provides web-based user interfaces and application programmable interfaces for searching and downloading STIX data products. The STIX Data Center has been operating successfully for more than two years. The platform facilitates instrument operations and provides vital support to STIX data users.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Andrew Inglis
Laura Hayes
Silvina Guidoni
James McLaughlin
Valery M. Nakariakov
Tom Van Doorsselaere
Ernesto Zurbriggen
Mariana Cécere
Marie Dominique
Jeff Reep
Ivan Zimovets
Elena Kupriyanova
Dmitrii Kolotkov
Bo Li
Marina Battaglia
Christopher Moore
Hannah Collier
Crisel Suarez
Tishtrya Mehta
Trevor Knuth
Abstract： Solar flares are among the most powerful and disruptive events in our solar system, however the physical mechanisms driving and transporting this energetic release are not fully understood. An important signature associated with flare energy release is highly variable emission on timescales of sub-seconds to minutes which often exhibit oscillatory behaviour, features collectively known as quasi-periodic pulsations (QPPs). To fully identify the driving mechanism of QPPs, exploit their potential as a diagnostic tool, and incorporate them into our understanding of solar and stellar flares, new observational capabilities and initiatives are required. There is a clear community need for flare-focused, rapid cadence, high resolution, multi-wavelength imaging of the Sun, with high enough sensitivity and dynamic range to observe small fluctuations in intensity in the presence of a large overall intensity. Furthermore, multidisciplinary funding and initiatives are required to narrow the gap between numerical models and observations. QPPs are direct signatures of the physics occurring in flare magnetic reconnection and energy release sites and hence are critical to include in a unified flare model. Despite significant modelling and theoretical work, no single mechanism or model can fully explain the presence of QPPs in flares. Moreover, it is also likely that QPPs fall into different categories that are produced by different mechanisms. At present we have insufficient information to observationally distinguish between mechanisms. The motivation to understand QPPs is strengthened by the geo-effectiveness of flares on the Earth's ionosphere, and by the fact that stellar flares exhibit similar QPP signatures. QPPs present a golden opportunity to better understand flare physics and exploit the solar-stellary analogy, benefiting both astrophysics, heliophysics, and the solar-terrestrial connection.
Peer Review Status:Awaiting Review
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