Space-based Solar Observatory Research Articles

Various Features of the X-class White-light Flares in Super Active Region NOAA 13664

Super active region NOAA 13664 produced 12 X-class flares (including the largest one so far, an occulted X8.7 flare, in solar cycle 25) during 2024 May 8–15, and 11 of them are identified as white-light flares. Here we present various features of these X-class white-light flares observed by the White-light Solar Telescope (WST) on board the Advanced Space-based Solar Observatory and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. It is found that both the white-light emissions at WST 3600 Å (Balmer continuum) and HMI 6173 Å (Paschen continuum) show up in different regions of the sunspot group in these flares, including outside the sunspots and within the penumbra and umbra of the sunspots. They exhibit a point-, ribbon-, loop-, or ejecta-like shape, which can come from flare ribbons (or footpoints), flare loops, and plasma ejecta depending on the perspective view. The white-light duration and relative enhancement are measured and both parameters for 3600 Å emission have greater values than those for 6173 Å emission. It is also found that these white-light emissions are cospatial well with the hard X-ray (HXR) sources in the on-disk flares but have some offsets with the HXR emissions in the off-limb flares. In addition, it is interesting that the 3600 and 6173 Å emissions show different correlations with the peak HXR fluxes, with the former one more sensitive to the HXR emission. All these greatly help us understand the white-light flares of a large magnitude from a super active region on the Sun and also provide important insights into superflares on Sun-like stars.

Inflight Performance and Calibrations of the Lyman-Alpha Solar Telescope on Board the Advanced Space-Based Solar Observatory

Inflight Performance and Calibrations of the Lyman-Alpha Solar Telescope on Board the Advanced Space-Based Solar Observatory

Carrington Maps in H i Lyα and Their Relationships with Extreme-ultraviolet and Magnetic-field Maps

H i Lyα emission in the chromosphere and transition region is a key ingredient of the incident radiation to coronal neutral hydrogen for modeling corona Lyα emission. The Lyα emission distribution across the solar disk can be obtained from a Lyα Carrington map. Before the launch of the Advanced Space-based Solar Observatory (ASO-S), such a Lyα Carrington map was derived from the Carrington map at He ii 30.4 nm and sometimes is even assumed to be uniform. We construct the first Lyα Carrington map based on full-disk Lyα images acquired by the Solar Disk Imager (SDI) on board ASO-S and present two versions: the standard one is for a CR, and the other is daily updated. For modeling Lyα intensities during eruptions, the Carrington map with incorporated flare region is produced. Furthermore, we evaluate the difference between the Lyα Carrington map derived with SDI observations and that synthesized from the 30.4 nm data based on an empirical relationship between Lyα and He ii 30.4 nm intensities, particularly extended to flare intensities that have not been investigated before. The average difference of 38% proves the importance of the Lyα Carrington map built from observations directly. However, the synthetic Lyα Carrington map can be used as an approximation before SDI data are available. The comparison between the SDI Lyα Carrington map and the corresponding magnetic field synoptic map indicates that active regions in general are brighter in Lyα, while the sunspot umbras with strong magnetic field strength are usually weaker in Lyα.

Electron acceleration and transport in the 2023-03-06 solar flare

We investigated in detail the M5.8 class solar flare that occurred on 2023-03-06. This flare was one of the first strong flares observed by the Siberian Radioheliograph in the microwave range and the Advanced Space-based Solar Observatory in the X-ray range. The flare consisted of two separate flaring events (a “thermal” and a “cooler” ones), and was associated with (and probably triggered by) a filament eruption. During the first part of the flare, the microwave emission was produced in an arcade of relatively short and low flaring loops. During the second part of the flare, the microwave emission was produced by energetic electrons trapped near the top of a large-scale flaring loop; the evolution of the trapped electrons was mostly affected by the Coulomb collisions. Using the available observations and the GX Simulator tool, we created a 3D model of the flare, and estimated the parameters of the energetic electrons in it.

Kink-and-Disconnection Failed Eruption in 3D

We present a case study of a failed eruption that accompanied an M1.5 GOES class solar flare. It was observed by STIX onboard Solar Orbiter, HXI onboard the Advanced Space-based Solar Observatory, AIA onboard Solar Dynamics Observatory, and WAVES onboard the STEREO-A. The important input is from stereoscopic hard X-ray (HXR) observations obtained by HXI and STIX, whose vantage points were separated by 31.5∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$31.5^{\\circ }$\\end{document}, allowing us to unfold the 3D geometry of the event. The eruption was a two-phase event. First, it started with the rope helical kink and then was slowed down, but with the structure still unstable, it erupted two minutes later due to ongoing reconnection in the interacting legs of the kinked structure. A Type III burst was observed in association with the eruption, indicating the acceleration of semirelativistic electrons into the heliosphere. During the second phase, a hot cloud was disconnected and confined in the overlying magnetic field, where the overlying loops connected two adjacent active regions. The estimated and corrected for real geometry velocities are in the range of 385 – 400 km s−1, whereas acceleration reached 4.78 – 6.33 km s−2. These extreme values are much more demanding from a perspective of conditions that are needed to stop the eruption. Images obtained simultaneously by HXI and STIX located in different vantage points showed that flare-related sources are not lying along a normal to the solar surface. The understanding of the eruption analyzed here has been highly enriched thanks to the stereoscopic information about HXR source locations.

Spectral and Imaging Observations of a C2.3 White-Light Flare from the Advanced Space-Based Solar Observatory (ASO-S) and the Chinese Hα\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\alpha $\\end{document}Solar Explorer (CHASE)

Solar white-light flares are characterized by an enhancement in the optical continuum, which are usually large flares (X- and M-class flares). Here, we report a small C2.3 white-light flare (SOL2022-12-20T04:10) observed by the Advanced Space-based Solar Observatory and the Chinese Hα\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\alpha $\\end{document}Solar Explorer (CHASE). This flare exhibits an increase of ≈ 6.4% in the photospheric Fe i line at 6569.2 Å and ≈ 3.2% in the nearby continuum. The continuum at 3600 Å also shows an enhancement of ≈ 4.7%. The white-light bright kernels are mainly located at the flare ribbons and co-spatial with nonthermal hard X-ray sources, which implies that the enhanced white-light emissions are related to nonthermal electron-beam heating. At the bright kernels, the Fe i line displays an absorption profile that has a good Gaussian shape, with a redshift up to ≈ 1.7 km s−1, while the Hα\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\alpha $\\end{document} line shows an emission profile having a central reversal. The Hα\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\alpha $\\end{document} line profile also shows a red or blue asymmetry caused by plasma flows with a velocity of several to tens of km s−1. It is interesting to find that the Hα\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\alpha $\\end{document} asymmetry is opposite at the conjugate footpoints. It is also found that the CHASE continuum increase seems to be related to the change in the photospheric magnetic field. Our study provides comprehensive characteristics of a small white-light flare that help understand the energy release process of white-light flares.

Automatic Solar Flare Detection Using the Solar Disk Imager Onboard the ASO-S Mission

We present an automated solar flare detection software tool to automatically process solar observed images, detect and track solar flares, and finally compile an event catalog. It can identify and track flares that happen simultaneously or temporally close together. The method to identify a flare is based on the local intensity changes in macropixels. The basic characteristics, such as the time and location information of a flare, are determined with a triple-threshold scheme, with the first threshold (global threshold) to determine the occurrence (location) of the flare and the second and third thresholds (local thresholds) to determine the real start and end times of the flare. We have applied this tool to one month of continuous solar ultraviolet (UV) images obtained by the Solar Disk Imager (SDI) onboard the Advanced Space-based Solar Observatory (ASO-S), which show active phenomena such as flares, filaments or prominences, and solar jets. Our automated tool efficiently detected a total number of 226 solar events. After a visual inspection, we found that only one event was misidentified (unrelated to an active event). We compared the detected events with the GOES X-ray flare list and found that our tool can detect 81% of GOES M-class and above flares (29 out of 36), from which we conclude that the intensity increase in SDI UV images can be considered as a good indicator of a solar flare.

Preliminary results for platform testing of ASO-S satellite

Advanced space-based solar observatory, which is short for ASO-S, was successfully launched by Chinese launcher CZ-2D in Oct. 2022. As of Dec. 13, 2022, the platform testing of the ASO-S satellite finished. The platform consists of seven main subsystems. The nominal specifications for every subsystem are laid out in detail in its technical document. The nominal specifications are used as a baseline to judge whether the in-orbit testing results are acceptable. The preliminary results include measurements for every specification for platform testing of the ASO-S satellite. The data analyses have shown that the performance of the main subsystems of the platform has Satisfied the specifications required by the technical documents. The platform performance has been demonstrated to be completely acceptable. The healthy platform performance of ASO-S will further support the payloads of the satellite in carrying out in-orbit observations of Solar activities.

The White-light Emissions in Two X-class Flares Observed by ASO-S and CHASE

The white-light continuum emissions in solar flares (i.e., white-light flares) are usually observed on the solar disk but, in a few cases, off the limb. Here we present on-disk as well as off-limb continuum emissions at 3600 Å (in the Balmer continuum) in an X2.1 flare (SOL2023-03-03T17:52) and an X1.5 flare (SOL2023-08-07T20:46), respectively, observed by the White-light Solar Telescope on the Advanced Space-based Solar Observatory. These continuum emissions are seen at the ribbons for the X2.1 flare and on loops during the X1.5 event, in which the latter also appears in the decay phase. These emissions also show up in the pseudocontinuum images at Fe i λ6173 from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory. In addition, the ribbon sources in the X2.1 flare exhibit significant enhancements in the Fe i line at 6569.2 Å and the nearby continuum observed by the Chinese Hα Solar Explorer. It is found that the on-disk continuum emissions in the X2.1 flare are related to a nonthermal electron-beam heating either directly or indirectly, while the off-limb emissions in the X1.5 flare are associated with thermal plasma cooling or due to Thomson scattering. These comprehensive continuum observations provide good constraints on flare energy deposition models, which helps us to better understand the physical mechanism of white-light flares.

A Statistical Study of Solar White-Light Flares Observed by the White-Light Solar Telescope of the Lyman-Alpha Solar Telescope on the Advanced Space-Based Solar Observatory (ASO-S/LST/WST) at 360 nm

Solar white-light flares (WLFs) are those accompanied by brightenings in the optical continuum or integrated light. The White-light Solar Telescope (WST), as an instrument of the Lyman-alpha Solar Telescope (LST) on the Advanced Space-based Solar Observatory (ASO-S), provides continuous solar full-disk images at 360 nm, which can be used to study WLFs. We analyze 205 major flares above M1.0 from October 2022 to May 2023 and identify 49 WLFs at 360 nm from WST observations, i.e. with an occurrence rate of 23.9%. The percentages of WLFs for M1 – M4 (31 out of 180), M5 – M9 (11 out of 18), and above X1 (7 for all) flares are 17.2%, 61.1%, and 100%, respectively, namely the larger the flares, the more likely they are WLFs at 360 nm. We further analyze 39 WLFs among the identified WLFs and investigate their properties such as white-light enhancement, duration, and brightening area. It is found that the relative enhancement of the white-light emission at 360 nm is mostly (>90%) less than 30% and the mean enhancement is 19.4%. The WLFs’ duration at 360 nm is mostly (>80%) less than 20 minutes and its mean is 10.3 minutes. The brightening area at 360 nm is mostly (>75%) less than 500 arcsecond2 and the median value is 225. We find that there exist good correlations between the white-light enhancement/duration/area and the peak soft X-ray (SXR) flux of the flare, with correlation coefficients of 0.68, 0.58, and 0.80, respectively. In addition, the white-light emission in most WLFs peaks around the same time as the temporal derivative of SXR flux as well as the hard X-ray emission at 20 – 50 keV, indicative of the Neupert effect. It is also found that the limb WLFs are more likely to have a greater enhancement, which is consistent with numerical simulations.

X-ray beam experiment for the Hard X-ray Imager onboard ASO-S

The Hard X-ray Imager (HXI) is one of the scientific payloads onboard the Advanced Space-based Solar Observatory. As a telescope using Fourier space modulation, it contains fine sub-collimators to reach high angular resolution. The X-ray resolution of HXI needs to be verified on the ground before its launch. Therefore, an X-ray beam experiment was performed to evaluate the modulation capabilities of each sub-collimator in HXI.The X-ray beam facility for this experiment consisted of an X-ray machine with a 0.4 mm-diameter spot, a 26-meter beam tube with an adjustable diaphragm at the end to control the parallelism of the beam, and an experimental platform that could translate and horizontally rotate the instrument on it with high precision. A strategy for measuring these sub-collimators was then developed theoretically. Additionally, the stability of the instrument and the environment were monitored throughout the experiment.The results of the successful experiment are presented in this paper. The relevant parameters fitted from the measured modulation functions agree well with theoretical predictions. This proves the resolving ability of the HXI meets the requirements. The research also illustrates some side effects due to different incident energies and strengtheners.

China’s First Comprehensive Space Solar Observatory

Being China’s first comprehensive space solar observatory, ASO-S (Advanced Space-based Solar Observatory) has been launched into orbit at 7:43 Beijing Time on October 9, 2022. A very brief introduction on ASO-S is presented here, including the background, scientific goals, payload deployments, mission assembly, and organizations. A short prospect is made for the operation of the mission and the future scientific output.

Construction and Validation of a Geometry-based Mathematical Model for the Hard X-Ray Imager

Quantitative and analytical analysis of the modulation process of the collimator is a great challenge, and is also of great value to the design and development of Fourier transform imaging telescopes. The Hard X-ray Imager (HXI), as one of the three payloads onboard the Advanced Space-based Solar Observatory (ASO-S) mission, adopts modulating Fourier-Transformation imaging technique and will be used to explore the mechanism of energy release and transmission in solar flare activities. As an important step to reconstruct the images of solar flares, accurate modulation functions of HXI are needed. In this paper, a mathematical model is developed to analyze the modulation function under a simplified condition first. Then its behavior under six degrees of freedom is calculated after adding the rotation matrix and translation change to the model. In addition, unparalleled light and extended sources are also considered so that our model can be used to analyze the X-ray beam experiment. Next, applied to the practical HXI conditions, the model has been confirmed not only by Geant4 simulations but also by some verification experiments. Furthermore, how this model helps to improve the image reconstruction process after the launch of ASO-S is also presented.

Calibration scheme for space-borne full-disk vector magnetograph under the influence of orbiter velocity

Context. The Full-disk Vector MagnetoGraph (FMG) is one of the three payloads on the Advanced Space-based Solar Observatory (ASO-S). The FMG is set to observe the full disk vector magnetic field at a single wavelength point. The magnetograph in orbit will encounter the wavelength shift problem caused by the Doppler effect in the magnetic field, which mainly comes from the Sun’s rotation velocity and the satellite–sun relative velocity. Aims. We look to use neural networks for single-wavelength calibration to solve the wavelength shift problem. Methods. We used the existing data from the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO). To simulate plausible single-wavelength observations, we used the Stokes polarization image from the HMI at a single wavelength point. We also input the satellite orbital velocity given by the HMI data file and the solar rotation velocity to the network. We developed a set of data preprocessing methods before entering the network and we trained the network to get the calibration model. Results. By analyzing and comparing the prediction of the neural network with the target magnetogram, we believe that our network model has learned a single-wavelength full-disk calibration model. The mean absolute error (MAE) of the longitudinal field and the transverse field of the full disk are 3.68 G and 28.08 G, respectively. The MAE error of the azimuth angle of pixels above 300 G is 12.29°.

Synthetic Lyman-α emissions for the coronagraph aboard the ASO-S mission

Context. Strong ultraviolet (UV) emission from the sun will be observed by the Lyman-α Solar Telescope (LST) on board the Advanced Space-based Solar Observatory (ASO-S), scheduled for launch in 2022. It will provide continuous observations from the solar disk to the corona below a 2.5 solar radius with high resolution. To configure the appropriate observing modes and also to better understand its upcoming observations, a series of simulations and syntheses of different structures and processes need to be done in advance. Aims. As prominence eruptions are the main drivers of space weather, the need to monitor such phenomena has been set as a priority among the objectives of ASO-S mission. In this work, we synthesize the evolution of a modeled prominence-cavity system before and during its eruption in the field of view (FOV) of LST. Methods. We adopted the input magnetohydrodynamic (MHD) model of a prominence-cavity system, which is readily comparable to the Atmospheric Imaging Assembly (AIA) observations. The Lyman-α emission of the prominence and its eruptive counterparts are synthesized through the PRODOP code, which considers non-local thermodynamic equilibrium (NLTE) radiative transfer processes, while the other coronal part such as the cavity and surrounding streamer, are synthesized with the FORWARD package, which deals with optically thin structures. Results. We present a discussion of the evolution of the eruptive prominence-cavity system, analyzing the synthetic emissions both on the disk near the limb and above the limb as viewed by the coronagraph, as well as the three-dimensional (3D) data of the MHD simulation. Conclusions. The evolution of the prominence-cavity system exhibits the condensation of cavity mass onto the prominence and the evaporation of prominence plasma into the central cavity. The synthetic emission in Lyman-α shows a similar pattern as in the AIA extreme ultraviolet (EUV) wavelengths before eruption, namely, the appearance of a “horn” substructure as a precursor to the eruption. The emission of prominence with an optically thick assumption is one to two orders of magnitude lower than the optically thin one. Here, the dimming effect in Lyman-α is analyzed, for the first time, for the eruptive prominence-cavity system. Accompanying the prominence plasma motion during the eruption, the apparent dimming shows a preferred location evolving from the top and bottom of the bright core to the whole body above the bottom part, while the collisional component progressively dominates the total emission of the flux rope bright core at these locations. By analyzing the signal-to-noise ratio (S/N) with a consideration of LST’s optical design, we conclude that the substructures in the cavity and the bright core of the CME can be observed with sufficient S/N at different stages in the FOV of LST.

Research on the On-orbit Background of the Hard X-Ray Imager Onboard ASO-S

The space environment background of various particle fluxes of the Hard X-ray Imager (HXI), one of the payloads of the Advanced Space-based Solar Observatory (ASO-S) spacecraft, is investigated and presented. Different approaches are used to obtain the input information on various space environment particles (protons, alpha particles, electrons, positrons, neutrons, and photons). Some special regions (SAA and radiation belt) are also taken into account. The findings indicate that electrons are the primary background source in the radiation belt. Due to the large background flux generated by electrons, HXI cannot effectively observe solar flares in the radiation belt. Outside the radiation belt, primary protons and albedo photons are the main sources of background at low and high magnetic latitudes respectively. The statistical analysis of the flare and background spectra shows that the errors of the flare energy spectrum observation are mainly concentrated in the high energy band, and the detector still has a certain spectrum observation capability for flares of C-class and below in the low energy band of the non-radiation belt. The imaging observation of flares of C-class and below is significantly affected by the accuracy of background subtraction. The energy band with the best signal-to-noise ratio is from 10 to 50 keV, which can be used to monitor the formation and class of flares.

The Aditya-L1 mission of ISRO

AbstractThe Aditya-L1 is the first space-based solar observatory of the Indian Space Research Organization (ISRO). The spacecraft will carry seven payloads providing uninterrupted observations of the Sun from the first Lagrangian point. Aditya-L1 comprises four remote sensing instruments, viz. a coronagraph observing in visible and infrared, a full disk imager in Near Ultra-Violet (NUV), and two full-sun integrated spectrometers in soft X-ray and hard X-ray. In addition, there are three instruments for in-situ measurements, including a magnetometer, to study the magnetic field variations during energetic events. Aditya-L1 is truly a mission for multi-messenger solar astronomy from space that will provide comprehensive observations of the Sun across the electromagnetic spectrum and in-situ measurements in a broad range of energy, including magnetic field measurements at L1.

Pre-launch characterization of the spectrometer of Hard X-ray Imager (HXI) onboard the ASO-S mission

As one of the three payloads of the Advanced Space-based Solar Observatory (ASO-S), the pre-launch characterization of HXI includes the characterization of the collimator and the spectrometer. This article focuses on the pre-launch characterization of HXI's spectrometer, including detection efficiency, energy resolution, and energy to ADC channel (E-C) relationship. The detection efficiency characterization necessitates a sufficient number of calibrated energy points in the HXI observation energy range, with a refined measurement around the absorption edge of the lanthanum bromide crystal, and is calibrated with an X-ray beam. The characterization results are consistent with the simulations and show that the detection efficiency difference between detector modules is controlled within ±3%. Radioactive sources 133Ba and 137Cs are used to calibrate the energy resolution and E-C relationship. The characterization results show that all detector modules' energy resolutions are better than 26% at 32 keV, meeting the design specification. And their E-C relationships vary regularly with voltage. All of the characterization results indicate that the flight model of the HXI spectrometer meets the performance requirements and is capable of performing on-orbit observation activities.

Design of front-end electronics for HXI spectrometer flight model on-board ASO-S satellite

Advanced Space-based Solar Observatory (ASO-S), developed by Chinese Academy of Sciences, is utilized for observing the solar magnetic field, coronal mass ejection, and solar flare, as well as studying the relationships among them. As one of the three scientific payloads on ASO-S, Hard X-ray Imager (HXI) is designed for solar hard X-ray imaging with outstanding temporal and spatial resolutions. The spectrometer is an important part of HXI and used to measure the incident photon with a dynamic range of 30–200 keV after Fourier modulation by the collimator. It consists of 99 detector units and front-end electronics (FEE). The FEE can process all the 99 detector units' signals independently in less than 2 μs. The noise of charge measure is less than 500 fC for a dynamic range of 20 pC–900 pC. In this paper, the implementation of FEE is introduced, including the design of electronics, quality control, and performance tests. All these tests show that the FEE can meet the HXI mission requirements.

SCSS-Net: solar corona structures segmentation by deep learning

ABSTRACT Structures in the solar corona are the main drivers of space weather processes that might directly or indirectly affect the Earth. Thanks to the most recent space-based solar observatories, with capabilities to acquire high-resolution images continuously, the structures in the solar corona can be monitored over the years with a time resolution of minutes. For this purpose, we have developed a method for automatic segmentation of solar corona structures observed in the EUV spectrum that is based on a deep-learning approach utilizing convolutional neural networks. The available input data sets have been examined together with our own data set based on the manual annotation of the target structures. Indeed, the input data set is the main limitation of the developed model’s performance. Our SCSS-Net model provides results for coronal holes and active regions that could be compared with other generally used methods for automatic segmentation. Even more, it provides a universal procedure to identify structures in the solar corona with the help of the transfer learning technique. The outputs of the model can be then used for further statistical studies of connections between solar activity and the influence of space weather on Earth.