本研究开发了一种利用 Solar Orbiter 的 STIX 高分辨率数据，通过高斯过程回归和高斯线性组合分解，系统探测和表征太阳耀斑非热硬 X 射线时间轮廓中快速变化（$\gtrsim 1$s）的新方法，并首次在 4-128s 时间尺度上成功探测到此类变化。
摘要：
目的：本工作旨在开发一种方法，利用 Solar Orbiter 的 X 射线成像光谱仪/望远镜（STIX）的高分辨率数据，系统地探测和表征太阳耀斑非热硬 X 射线（HXR）时间轮廓中的快速时间变化（$\gtrsim 1$s）。\n方法：使用高斯过程（GP）回归对 HXR 时间轮廓进行平滑处理。随后用高斯函数的线性组合拟合时间轮廓以进行分解。从高斯分解中，可以推导出周期性、半高全宽（FWHM）、时间演化和振幅等关键特征。\n结果：我们展示了将该方法应用于 Solar Orbiter 科学运行第一年期间发生的四次 M 级和 X 级 GOES 分类耀斑的结果。这些耀斑的 HXR 时间轮廓被分解为单个高斯分量，并推导了它们的周期。拟合质量通过残差的标准差（即观测曲线与拟合曲线之差除以观测数据误差）来量化，对于本文展示的所有耀斑，该值 $\leq 1.8$。在本研究中，首次利用 Solar Orbiter 的 STIX 仪器在 4-128s 范围的时间尺度上探测到了快速时间变化。\n结论：我们开发了一种识别和表征太阳耀斑非热 HXR 轮廓中快速时间变化的新方法，该方法使用高斯爆发的线性组合拟合时间轮廓。借助 Solar Orbiter 上 STIX 的最新观测数据，研究耀斑时间变化的能力得到了极大提升。
英文摘要：
Aims: The aim of this work is to develop a method to systematically detect and characterise fast-time variations ($\gtrsim 1$s) in the non-thermal hard X-ray (HXR) time profiles of solar flares using high-resolution data from Solar Orbiter's Spectrometer/Telescope for Imaging X-rays (STIX).
Methods: The HXR time profiles were smoothed using Gaussian Process (GP) regression. The time profiles were then fitted with a linear combination of Gaussians to decompose the time profile. From the Gaussian decomposition, key characteristics such as the periodicity, full width at half maximum (FWHM), time evolution, and amplitude can be derived.
Results: We present the outcome of applying this method to four M and X GOES-class flares from the first year of Solar Orbiter science operations. The HXR time profiles of these flares were decomposed into individual Gaussians and their periods were derived. The quality of fit is quantified by the standard deviation of the residuals (difference between observed and fitted curve, normalised by the error on the observed data), for which we obtain $\leq 1.8$ for all flares presented. In this work, the first detection of fast-time variations with Solar Orbiter's STIX instrument has been made on timescales across the range of 4-128s.
Conclusions: A new method for identifying and characterising fast-time variations in the non-thermal HXR profiles of solar flares has been developed, in which the time profiles are fit with a linear combination of Gaussian bursts. The opportunity to study time variations in flares has greatly improved with the new observations from STIX on Solar Orbiter.
The Spectrometer/Telescope for Imaging X-rays (STIX) is a hard X-ray imaging spectroscopy device to be mounted in the Solar Orbiter cluster with the aim of providing images and spectra of solar flaring regions at different photon energies in the range from a few keV to around 150 keV. The imaging modality of this telescope is based on the Moire pattern concept and utilizes 30 sub-collimators, each one containing a pair of co-axial grids. This paper applies Fourier analysis to provide the first rigorous description of the data formation process in STIX. Specifically, we show that, under first h…
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 GOE…
The Spectrometer/Telescope for Imaging X-rays (STIX) will look at solar flares across the hard X-ray window provided by the Solar Orbiter cluster. Similarly to the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), STIX is a visibility-based imaging instrument, which will ask for Fourier-based image reconstruction methods. However, in this paper we show that, as for RHESSI, also for STIX count-based imaging is possible. Specifically, here we introduce and illustrate a mathematical model that mimics the STIX data formation process as a projection from the incoming photon flux into a…
Context. The Spectrometer/Telescope for Imaging X-rays (STIX) is one of 6 remote sensing instruments on-board Solar Orbiter. It provides hard X-ray imaging spectroscopy of solar flares by sampling the Fourier transform of the incoming flux. Aims. To show that the visibility amplitude and phase calibration of 24 out of 30 STIX sub-collimators is well advanced and that a set of imaging methods is able to provide the first hard X-ray images of the flaring Sun from Solar Orbiter. Methods. We applied four visibility-based image reconstruction methods and a count-based one to calibrated STIX observa…
Responses of the X-ray spectrometer/imager STIX onboard Solar Orbiter
University of Applied Sciences and Arts Northwestern Switzerland (FHNW)（西北瑞士应用科学与艺术大学）；The Physical Meteorological Observatory and World Radiation Center (PMOD/WRC)（物理气象观测站与世界辐射中心）；IRFU, CEA, Université Paris-Saclay and Université Paris Diderot, AIM, Sorbonne Paris Cité, CEA, CNRS（IRFU、CEA、巴黎萨克雷大学和巴黎第七大学、AIM、索邦巴黎西大、CEA、CNRS）
During the next solar maximum, two upcoming space-borne X-ray missions, STIX on board Solar Orbiter and MiSolFA, will perform stereoscopic X-ray observations of solar flares at two different locations: STIX at 0.28 AU (at perihelion) and up to inclinations of $\sim25^{\circ}$, and MiSolFA in a low-Earth orbit. The combined observations from these cross-calibrated detectors will allow us to infer the electron anisotropy of individual flares confidently for the first time. We simulated both instrumental and physical effects for STIX and MiSolFA including thermal shielding, background and X-ray C…
Multi-point study of the energy release and transport in the 28 March 2022, M4-flare using STIX, EUI, and AIA during the first Solar Orbiter nominal mission perihelion
Aima. To determine to what extent the problem of forward fitting visibilities measured by the Spectrometer/Telescope Imaging X-rays (STIX) on-board Solar Orbiter is more challenging with respect to the same problem in the case of previous hard X-ray solar imaging missions; to identify an effective optimization scheme for parametric imaging for STIX. Methods. This paper introduces a Particle Swarm Optimization (PSO) algorithm for forward fitting STIX visibilities and compares its effectiveness with respect to the standard simplex-based optimization algorithm used so far for the analysis of visi…
Solar flares are the most powerful events in the solar system and the brightest sources of X-rays, often associated with emission of particles reaching the Earth and causing geomagnetic storms, giving problems to communication, airplanes and even black-outs. X-rays emitted by accelerated electrons are the most direct probe of solar flare phenomena. The Micro Solar-Flare Apparatus (MiSolFA) is a proposed compact X-ray detector which will address the two biggest issues in solar flare modeling. Dynamic range limitations prevent simultaneous spectroscopy with a single instrument of all X-ray emitt…
During its commissioning phase in 2020, the Spectrometer/Telescope for Imaging X-rays (STIX) on board the Solar Orbiter spacecraft observed 69 microflares. The two most significant events from this set (of GOES class B2 and B6) were observed on-disk from the spacecraft as well as from Earth and analysed in terms of the spatial, temporal, and spectral characteristics. We complement the observations from the STIX instrument with EUV imagery from SDO/AIA and GOES soft X-ray data by adding imaging and plasma diagnostics over different temperature ranges for a detailed microflare case study that is…
Triple coronal hard X-ray source observed by STIX during a failed filament eruption
Space Research Centre, Polish Academy of Sciences（波兰科学院空间研究中心）；Astronomical Institute, University of Wrocław（弗罗茨瓦夫大学天文研究所）；ETH-Zürich（苏黎世联邦理工学院）；PMOD/WRC（帕默尔太阳物理观测站/世界辐射中心）
First results from PADRE/MeDDEA: X-rays from a flare and its CME
University of Applied Sciences and Arts Northwestern Switzerland（西北瑞士应用科学与艺术大学）；ETH Zürich（苏黎世联邦理工学院）；Université Paris-Saclay（巴黎萨克雷大学）；Université Paris Cité（巴黎西岱大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；American University（美利坚大学）；Southwest Research Institute（西南研究所）；Space Sciences Laboratory, University of California（加州大学空间科学实验室）
Solar Orbiter observations of solar energetic electron events associated with hard microflares
ETH-Zürich（苏黎世联邦理工学院）；Istituto ricerche solari Aldo e Cele Daccò (IRSOL), Faculty of Informatics, Università della Svizzera Italiana（瑞士意大利大学信息学院阿尔多和塞莱达科太阳研究所）；European Space Agency (ESA), European Space Astronomy Centre (ESAC)（欧洲空间局欧洲空间天文中心）；Universidad de Alcalá（阿卡拉大学）；PMOD/WRC（帕尔默气象观测站/世界辐射中心）
University of Applied Sciences and Arts Northwestern Switzerland（西北瑞士应用科学与艺术大学）；Institute for Particle Physics and Astrophysics, ETH Zürich（苏黎世联邦理工学院粒子物理与天体物理研究所）；School of Physics & Astronomy, University of Glasgow（格拉斯哥大学物理与天文学学院）；Space Sciences Laboratory, University of California（加州大学空间科学实验室）
Elemental Composition Evolution during the 2024 September 30 Solar Eruption: A Comparison of Hot and Cool Plasma Components with Solar Orbiter/SPICE, Hinode/EIS, and Chandrayaan-2/XSM
Southwest Research Institute（西南研究所）；Ann and H.J. Smead Aerospace Engineering Sciences, University of Colorado Boulder（科罗拉多大学博尔德分校安与H.J.斯梅德航空航天工程科学系）；Laboratory for Atmospheric and Space Physics, University of Colorado Boulder（科罗拉多大学博尔德分校大气与空间物理实验室）；University of Alabama in Huntsville（阿拉巴马大学亨茨维尔分校）；NASA Marshall Space Flight Center（美国国家航空航天局马歇尔太空飞行中心）
Fine-scale flare structures and their energetic implications from short-exposure extreme-ultraviolet imaging
Dublin Institute for Advanced Studies（都柏林高等研究院）；University of Applied Sciences and Arts Northwestern Switzerland（瑞士西北应用科学艺术大学）；University of Toronto（多伦多大学）；Canadian Institute for Theoretical Astrophysics（加拿大理论天体物理研究所）；Space Sciences Laboratory, University of California（加州大学空间科学实验室）；University College London（伦敦大学学院）；Royal Observatory of Belgium（比利时皇家天文台）；ETH Zürich（苏黎世联邦理工学院）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）
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…
Stereoscopic Observations of Solar X-ray Sources Explained by a Data-Constrained Magnetohydrodynamic Simulation
New Jersey Institute of Technology（新泽西理工学院）；University of Applied Sciences and Arts Northwestern Switzerland（西北瑞士应用科学与艺术大学）；Space Sciences Laboratory, University of California（加州大学空间科学实验室）；Institute for Space-Earth Environmental Research, Nagoya University（名古屋大学地球·宇宙环境研究所）；ETH Zürich（苏黎世联邦理工学院）
We present the Fermi-LAT observations of the behind-the-limb (BTL) flare of July 17, 2021 and the joint detection of this flare by STIX onboard Solar Orbiter. The separation between Earth and the Solar Orbiter was 99.2$^{\circ}$ at 05:00 UT, allowing STIX to have a front view of the flare. The location of the flare was ~S20E140 in Stonyhurst heliographic coordinates making this the most distant behind-the-limb flare ever detected in $>$100 MeV gamma-rays. The LAT detection lasted for $\sim$16 minutes, the peak flux was $ 3.6 \pm 0.8 $ (10$^{-5}$) ph cm$^{-2}$ s$^{-1}$ with a significance $>$15…
CoSEE-Cat: A Comprehensive Solar Energetic Electron event Catalogue obtained from combined in situ and remote-sensing observations from Solar Orbiter -- Catalogue description and first statistical results
University of Applied Sciences and Arts Northwestern Switzerland（西北瑞士应用科学与艺术大学）；ETH Zürich（苏黎世联邦理工学院）；Università di Genova（热那亚大学）；Space Sciences Laboratory, University of California（加州大学空间科学实验室）
Three-dimensional mapping of coronal magnetic field and plasma parameters in a solar flare
Institut für Sonnenphysik (KIS)（太阳物理研究所）；Center For Solar-Terrestrial Research, New Jersey Institute of Technology（新泽西理工学院太阳-地球关系研究中心）；University College London, Mullard Space Science Laboratory（伦敦大学学院穆拉德太空科学实验室）
Count-based spectral component imaging (CCI) of solar flares in X-rays
Università di Genova（热那亚大学）；University of Applied Sciences and Arts Northwestern Switzerland（瑞士西北应用科学艺术大学）；ETH Zürich（苏黎世联邦理工学院）；Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino（意大利国家天体物理研究所都灵天文台）
The Micro Solar-Flare Apparatus (MiSolFA) is a compact X-ray imaging spectrometer designed for a small 6U micro-satellite. As a relatively inexpensive yet capable Earth-orbiting instrument, MiSolFA is designed to image the high-energy regions of solar flares from a different perspective than that of Solar Orbiter's STIX, operating from a highly elliptical heliocentric orbit. Two instruments working together in this way would provide a 3-dimensional view of X-ray emitting regions and can bypass the dynamic range limitation preventing simultaneous coronal and chromospheric imaging. Stereoscopic …
Maximum Entropy is an image reconstruction method conceived to image a sparsely occupied field of view and therefore particularly appropriate to achieve super-resolution effects. Although widely used in image deconvolution, this method has been formulated in radio astronomy for the analysis of observations in the spatial frequency domain, and an Interactive Data Language (IDL) code has been implemented for image reconstruction from solar X-ray Fourier data. However, this code relies on a non-convex formulation of the constrained optimization problem addressed by the Maximum Entropy approach an…
Context. We present an analysis of a GOES M1.8 flare with excellent observational coverage in UV, EUV, and X-ray, including observations from the instruments IRIS, SDO with AIA, Hinode/EIS, Hinode/XRT, and Solar Orbiter with the Spectrometer/Telescope for Imaging X-rays (STIX). Hard X-ray emission is often observed at the footpoints of flare loops and is occasionally observed in the corona. In this flare, four nonthermal hard X-ray sources are seen. Aim. Our aim is to understand why we can observe four individual nonthermal sources in this flare and how we can characterize the physical propert…
