Solar X-ray Research Articles

Enhanced stability and performance of perovskite solar cells and X-ray detectors via MoS2@MoO3 composites integration

Enhanced stability and performance of perovskite solar cells and X-ray detectors via MoS2@MoO3 composites integration

Tests of Solar X-ray Image Reconstruction: Study of X-ray Imaging Algorithms and Reconstruction Parameters

Abstract Abstract Imaging observations of solar X-ray bursts can reveal details of the energy release process and particle acceleration in flares. Most hard X-ray imagers make use of the modulation-based Fourier transform imaging method, an indirect imaging technique that requires algorithms to reconstruct and optimize images. During the last decade, a variety of algorithms have been developed and improved. However, it is difficult to quantitatively evaluate the image quality of different solutions without a true, reference image of observation. How to choose the values of imaging parameters for these algorithms to get the best performance is also an open question. In this study, we present a detailed test of the characteristics of these algorithms, imaging dynamic range and a crucial parameter for the CLEAN method, clean beam width factor (CBWF). We first used SDO/AIA EUV images to compute DEM maps and calculate thermal X-ray maps. Then these realistic sources and several types of simulated sources are used as the ground truth in the imaging simulations for both RHESSI and ASO-S/HXI. The different solutions are evaluated quantitatively by a number of means. The overall results suggest that EM, PIXON, and CLEAN are exceptional methods for sidelobe elimination, producing images with clear source details. Although MEM_GE, MEM_NJIT, VIS_WV and VIS_CS possess fast imaging processes and generate good images, they too possess associated imperfections unique to each method. The two forward fit algorithms, VF and FF perform differently, and VF appears to be more robust and useful. We also demonstrated the imaging capability of HXI and available HXI algorithms. Furthermore, the effect of CBWF on image quality was investigated, and optimal settings for both RHESSI and HXI were proposed.

Design and Test of a Calibration System for Avalanche Photodiodes Used in X-Ray Compton Polarimeters for Space.

The development and calibration of a measurement system designed for assessing the performance of the avalanche photodiodes (APDs) used in the Compton scattering polarimeter of the CUSP project is discussed in this work. The designed system is able to characterize the APD gain GAPD and energy resolution across a wide range of temperatures T (from -20 °C to +60 °C) and bias voltages Vbias (from 260 V to 410 V). The primary goal was to experimentally determine the GAPD dependence on the T and Vbias in order to establish a strategy for stabilizing GAPD by compensating for T fluctuations, acting on Vbias. The results demonstrate the system capability to accurately characterize APD behavior and develop feedback mechanisms to ensure its stable operation. This work provides a robust framework for calibrating APDs for space environments. It is essential for the successful implementation of spaceborne polarimeters such as the Compton scattering polarimeter foreseen aboard the CUbeSat Solar Polarimeter (CUSP) mission under development to perform solar flare X-ray polarimetry.

Calibration of the Solar X-ray Detector on-board the Macao Science Satellite-1B for Soft X-ray Detection

Calibration of the Solar X-ray Detector on-board the Macao Science Satellite-1B for Soft X-ray Detection

A New Solar Hard X-ray Image Reconstruction Algorithm for ASO-S/HXI Based on Deep Learning

A New Solar Hard X-ray Image Reconstruction Algorithm for ASO-S/HXI Based on Deep Learning

Design and technology review of the solar X-ray detector onboard the Macao Science Satellite-1B

Design and technology review of the solar X-ray detector onboard the Macao Science Satellite-1B

Short-wave fadeout on mars: Radio absorption in the dayside martian ionosphere enhanced by solar flares

Solar flares can cause radio absorption in the D region of the Earth’s ionosphere and consequently interrupt high-frequency radio communication systems, also known as short-wave fadeout or the Dellinger effect. We present an analogous radio absorption event observed at Mars during a solar flare. In this event, the Mars Express Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument fortuitously operated at low altitudes on the dayside around the terminator in a favorable configuration for surface echo measurements at the flare peak. The surface echo power during the flare is abnormally weak compared to nominal echo powers at corresponding solar zenith angles, suggesting flare-induced radio absorption in the dayside lower ionosphere of Mars. Additionally, long-term MARSIS data statistically demonstrate the radio absorption dependence on solar soft X-ray fluxes. Our results point to the need for Martian space weather prediction including ionospheric effects on radio waves.

Enhancing the X-ray Sensitivity of Cs2AgBiBr6 Double Perovskite Single Crystals through Cation Engineering.

Owing to their outstanding optoelectronic properties, halide perovskite (HP) materials have been employed in a wide range of applications, including solar cells, light-emitting devices, and X-ray detectors. Among them, lead-free double HPs are characterized by enhanced stability and reduced toxicity compared with lead-based alternatives. Cs2AgBiBr6, in particular, has emerged as a promising candidate for direct X-ray detection. The detection sensitivity, on the other hand, cannot yet compete with that of lead-containing perovskites. Developing schemes to improve X-ray detection efficiency is critical for reducing radiation exposure in medical imaging applications. Here, we investigate the potential of controlled doping and cation substitution with either lanthanides or small organic cations to improve the X-ray detection performance of Cs2AgBiBr6. Our findings reveal that by growing the perovskite in a slightly Bi-poor and Eu-rich environment, the X-ray sensitivity significantly increases 7-fold (from 17 to 120 μC Gyair -1 cm-2) and simultaneously improves the phototo-dark current ratio (from 2.5 to 29). Additionally, Cs-site substitution with imidazolium remarkably enhances the sensitivity over 10-fold (180 μC Gyair -1 cm-2), and ammonium enhances the phototo-dark current ratio to 37. Terahertz photoconductivity measurements reveal a positive correlation between enhanced X-ray sensitivity and improved charge transport properties (e.g., increased scattering time and, thus, carrier mobility) by doping. This study outlines straightforward strategies for boosting X-ray detection and fundamental photoconductivity in lead-free double HP, with potential implications for broader optoelectronic applications.

Dopant compensation in component-dependent self-doped Cs2SnI6 thin films grown with PLD at room temperature

Tetravalent tin (Sn4+)-based inorganic perovskite semiconductors like Cs2SnI6 are expected to replace lead-based perovskite counterparts due to advantages such as structural stability and environmental friendliness. In this paper, we reported the dopant compensation effect in the component-dependent self-doped (111)-oriented Cs2SnI6 thin films grown with pulsed laser deposition (PLD) at room temperature. The films were grown on (100)-SrTiO3 (STO) substrates at room temperature by PLD. Hall results of the Cs2SnI6 films with different components realizing by controlling the ratio of SnI4/CsI in the targets demonstrate a clear change of conductivity type from N-type to P-type, while the carrier concentration decreases from 1018 to 1013 and accordingly the film resistivity increases significantly from 3.8 to 2506 Ω cm. The defect-related optical fingerprints of Cs2SnI6 films were also investigated with temperature-dependent photoluminescence spectroscopy. At low temperatures of 10 K, the Cs2SnI6 films exhibit donor-bound (D0X) and donor-acceptor pair (DAP) emission, respectively, due to the self-doping effect. These results indicate that controlling the composition of the PLD target is a powerful way to tune the electrical properties of Cs2SnI6 films for possible applications in solar cells or X-ray detectors.

The Solar Aspect System of the Hard X-ray Imager Onboard ASO-S

The ASO-S/HXI is a bi-grids modulating instrument for solar hard X-ray imaging, whose collimator contains 91 pairs of tungsten grids. Since the solar disk is invisible in hard X-rays, a Solar Aspect System (SAS) is required to provide the pointing of hard X-ray imager (HXI) for locating X-ray sources on the solar disk. In addition, the knowledge of the alignment and relative twist of the corresponding front–rear grid pairs is important for image reconstruction as well as locating flares. Therefore, the SAS system was designed to monitor the alignment status of HXI grids and to provide the pointing direction of the HXI collimator with two subsystems DM and SA during the whole life cycle of HXI. DM measures the centroids of the front frosted glasses and the solar disk. SA images the Sun and provides precise relative locations of the solar disk center. Both work in the visible light of 565–585 nm. With all the data together, we can solve with an inversion algorithm the alignment status of the front and rear grids, the relative twist, and the pointing direction. We tested and validated the SAS design with both the simulation model and ground coordinate measuring machine. Here we present the detailed system design, the testing results, the inversion algorithm, and the in-orbit status of the SAS. Currently, the SAS has realized the rotational measurement accuracy of about 4 arcsec, and a translational measurement accuracy of about 15 μm, and the SAS pointing data has been used in both imaging calibration for flare locations and imaging corrections for the platform drifting effect. The high-cadence precise measurement (better than 0.3 arcsec) of the pointing will allow the study of source locations at different energies and therefore help us to understand electron acceleration and transportation in flares.

Adsorption of natural dye phycocyanin by means of Laponite®: Synthesis and characterization of the hybrid obtained

This work addresses the use of Laponite® clay in various applications, focusing on its adsorption capacity and improvement of properties in water-based products. It describes the synthesis of Laponite® hybrids with the pigmented cyanobacterium phycocyanin (PC) to evaluate the adsorption capacity of the dye. This research addresses the importance of Laponite® clay in improving rheological properties of water-based products due to its ability to interact with components in aqueous solutions. Laponite® can be effectively dispersed in water, enhancing the dispersion of other elements in solution and preventing aggregation of solids. The structure and properties of synthetic Laponite® are described, highlighting its use in the textile industry as an additive for pigments and the formation of gels. Experimentally, Laponite® is used to adsorb phycocyanin, a cyanobacterial pigment, with the aim of achieving maximum adsorption. A design of experiments with different experimental conditions, including pH, addition of silane and surfactant, is used. A detailed analysis of the characterization of the resulting hybrids is presented, including colour, total solar reflectance (TSR), thermal analysis (TGA), EDS, FTIR and X-ray diffraction (XRD) measurements. The results show successful adsorption of the pigment in all experiments, with adsorption percentages above 97%. The colour of the hybrids is evaluated and the total solar reflectance is analyzed, highlighting their importance in applications such as coatings and printed textiles. Infrared spectroscopy and X-ray diffraction are used to study the structural properties of the hybrids. For future work, it is intended to be able to apply the hybrids obtained on an industrial scale in the colouring of textiles and plastic polymers.

Unveiling Mass Transfer in Solar Flares: Insights from Elemental Abundance Evolutions Observed by Chang’E-2 Solar X-Ray Monitor

Understanding how elemental abundances evolve during solar flares helps shed light on the mass and energy transfer between different solar atmospheric layers. However, prior studies have mostly concentrated on averaged abundances or specific flare phases, leaving a gap in exploring the comprehensive observations throughout the entire flare process. Consequently, investigations into this area are relatively scarce. Exploiting the Solar X-Ray Monitor data obtained from the Chang’E-2 lunar orbiter, we present two comprehensive soft X-ray spectroscopic observations of flares in active regions, AR 11149 and 11158, demonstrating elemental abundance evolutions under different conditions. Our findings unveil the inverse first ionization potential (IFIP) effect during flares for Fe for the first time, and reaffirm its existence for Si. Additionally, we observed a rare depletion of elemental abundances, marking the second IFIP effect in flare decay phases. Our study offers a CSHKP model-based interpretation to elucidate the formation of both the FIP and IFIP effects in flare dynamics, with the inertia effect being incorporated into the ponderomotive force fractionation model.

Triangulation of Hard X-Ray Sources in an X-Class Solar Flare with ASO-S/HXI and Solar Orbiter/STIX

HXI on ASO-S and STIX onboard Solar Orbiter are the first simultaneously operating solar hard X-ray imaging spectrometers. ASO-S’s low Earth orbit and Solar Orbiter’s periodic displacement from the Sun–Earth line enables multi-viewpoint solar hard X-ray spectroscopic imaging analysis for the first time. Here, we demonstrate the potential of this new capability by reporting the first results of 3D triangulation of hard X-ray sources in the SOL2023-12-31T21:55 X5 flare. HXI and STIX observed the flare near the east limb with an observer separation angle of 18°. We triangulated the brightest regions within each source, which enabled us to characterise the large-scale hard X-ray geometry of the flare. The footpoints were found to be in the chromosphere within uncertainty, as expected, while the thermal looptop source was centred at an altitude of 15.1 ± 1 Mm. Given the footpoint separation, this implies a more elongated magnetic-loop structure than predicted by a semi-circular model. These results show the strong diagnostic power of joint HXI and STIX observations for understanding the 3D geometry of solar flares. We conclude by discussing the next steps required to fully exploit their potential.

Searching for Rapid Pulsations in Solar Flare X-Ray Data

Most studies of quasiperiodic pulsations (QPPs) in solar flares have identified characteristic periods in the 5–300 s range. Due to observational limitations, there have been few attempts to probe the <5 s period regime and understand the prevalence of such short-period QPPs. However, the Fermi Gamma-ray Burst Monitor (GBM) has observed approximately 1500 solar flares to date in high-cadence 16 Hz burst mode, providing us with an opportunity to study short-period QPPs at X-ray energies. We systematically analyze every solar flare observed by Fermi/GBM in burst mode, estimating the prevalence of QPPs in multiple X-ray energy bands. To better understand these results, we complement this with an analysis of synthetic solar flare lightcurves, both with and without oscillatory signals present. Using these synthetic lightcurves, we can understand the likely false-alarm and true-positive rates in the real solar GBM data. We do not find strong evidence for widespread short-period QPPs, indicating either a low base occurrence rate of such signatures or that their typical signal-to-noise ratios must be low—less than 1—in Fermi/GBM data. Finally, we present a selection of the most interesting potential QPP events that were identified in the GBM solar X-ray data.

An impulsive geomagnetic effect from an early-impulsive flare

ABSTRACT The geomagnetic ‘solar flare effect’ (SFE) results from excess ionization in the Earth’s ionosphere, famously first detected at the time of the Carrington flare in 1859. This indirect detection of a flare constituted one of the first cases of ‘multimessenger astronomy’, whereby solar ionizing radiation stimulates ionospheric currents. Well-observed SFEs have few-minute time-scales and perturbations of &amp;gt;10 nT, with the greatest events reaching above 100 nT. In previously reported cases, the SFE time profiles tend to resemble those of solar soft X-ray emission, which ionizes the D-region; there is also a less-well-studied contribution from Lyman α. We report here a specific case, from flare SOL2024-03-10 (M7.4), in which an impulsive SFE deviated from this pattern. This flare contained an ‘early impulsive’ component of exceptionally hard radiation, extending up to γ-ray energies above 1 MeV, distinctly before the bulk of the flare soft X-ray emission. We can characterize the spectral distribution of this early-impulsive component in detail, thanks to the modern extensive wavelength coverage. A more typical gradual SFE occurred during the flare’s main phase. We suggest that events of this type warrant exploration of the solar physics in the ‘impulse response’ limit of very short time-scales.

Photoexcited charge-carrier transport in monolayer and bulk bismuth oxyiodide: the impact of the polaronic effect and deep-level defects

Bismuth oxyiodide (BiOI), in monolayer and bulk forms, is a lead-free semiconductor material that has sparked increased interest for applications in perovskite solar cells and x-ray detectors. It is vital to clarify the transport nature of photoexcited charge-carriers to improve device performance. However, the transport scattering mechanisms remain poorly understood, and a detailed explanation of the measured charge-carrier mobilities in this material system is still under scrutiny. Herein, we implement transport scattering models that include LO phonon scattering based on the polaronic effect and ionized impurity scattering due to deep-level defects to elucidate photoexcited charge mobilities. We found that large polarons produced by photoexcited charge carriers coupled with LO phonon modes of 86 cm−1 and 156 cm−1 play a key role in the transport process of the BiOI system. Large polaron mobility provides a good explanation for the measured mobilities in single crystal samples between 26–83 cm2V−1s−1 at 295 K. The estimated results from both transport scattering models agree with the temperature-dependent mobilities measured in thin-film samples, between 13 cm2V−1s−1 at 5 K and 3 cm2V−1s−1 at 295 K. This work provides important insights into a band-like transport feature in the BiOI system.

Overview of the Space Weather Impact on the Navigation and Communication Systems

This article summarizes and analyzes the space weather impact on the Earth´s surface, aviation – especially navigation and communication aids, satellite functions ensuring communication, and GPS function. Forecasting the geomagnetic storms, solar radiation storms, radio blackouts, X-ray flux, and others is difficult due to the high variability of the space weather conditions and sun activity. It can change every hour and the exact space weather conditions and the impact on aviation for the future are hard to predict. This article shows some predictions and historical data regarding space weather activity, where the stated values were collected from the NOAA page. The article states the daily maximums or the maximums of predicted phenomena activity. Because of the complexity and the facts mentioned above, the historical data and predictions show the summary and most important phenomena of the day. The article consists of 3 main chapters: 1. Space Weather 2. Space Weather Impact on Technological Vulnerability 3. Space Weather Condition Overview in Data. The last chapter in this article is a conclusion that consists of and mentions some information about the used alternative methods when a GPS lapse occurs. Even though there are some alternate systems, but still using satellite-based navigation and communication aids is still the first option, and space weather events highly affect the systems and are a big hazard for aviation.

About the Possible Solar Nature of the ~200 yr (de Vries/Suess) and ~2000–2500 yr (Hallstadt) Cycles and Their Influences on the Earth’s Climate: The Role of Solar-Triggered Tectonic Processes in General “Sun–Climate” Relationship

(1) Introduction: The subject of the present study concerns the analysis of the existence and long time evolution of the solar ~200 yr (de Vries/Suess) and ~2400 yr (Hallstadt) cycles during the recent part of the Wurm ice epoch and the Holocene, as well as their forcing on the regional East European climate during the last two calendar millennia. The results obtained here are compared with those from our previous studies, as well as with the results obtained by other authors and with other types of data. A possible scenario of solar activity changes during the 21st century, as well as different possible mechanisms of solar–climatic relationships, is discussed. (2) Data and methods: Two types of indirect (historical) data series for solar activity were used: (a) the international radiocarbon tree ring series (INTCAL13) for the last 13,900 years; (b) the Schove series of the calendar years of minima and maxima and the magnitudes of 156 quasi 11 yr sunspot Schwabe–Wolf cycles since 296 AD and up to the sunspot cycle with number 24 (SC24) in the Zurich series; (c) manuscript messages about extreme meteorological and climatic events (Danube and Black Sea near-coast water freezing), extreme summer droughts, etc., in Bulgaria and adjacent territories since 296 and up to 1899 AD, when the Bulgarian meteorological dataset was started. A time series analysis and χ2-test were used. (3) Results and analysis: The amplitude modulation of the 200 yr solar cycle by the 2400 yr (Hallstadt) cycle was confirmed. Two groups of extremely cold winters (ECWs) during the last ~1700 years were established. Both groups without exclusion are concentrated near 11 yr sunspot cycle extremes. The number of ECWs near sunspot cycle minima is about 2 times greater than that of ECWs near sunspot cycle maxima. This result is in agreement with our earlier studies for the instrumental epoch since 1899 AD. The driest “spring-summer-early autumn” seasons in Bulgaria and adjacent territories occur near the initial and middle phases of the grand solar minima of the Oort–Dalton type, which relate to the downward phases and minima of the 200 yr Suess cycle. (4) Discussion: The above results confirm the effect of the Sun’s forcing on climate. However, it cannot be explained by the standard hypothesis for total solar irradiation (TSI) variations. That is why another hypothesis is suggested by the author. The mechanism considered by Svensmark for galactic cosmic ray (GCR) forcing on aerosol nuclei was taken into account. However, in the hypothesis suggested here, the forcing of solar X-ray flux changes (including solar flares) on the low ionosphere (the D-layer) and following interactions with the Earth’s lithosphere due to the terrestrial electric current systems play a key role for aerosol nuclei and cloud generation and dynamics during sunspot maxima epochs. The GCR flux maximum absorption layer at heights of 35–40 km replaces the ionosphere D-layer role during the sunspot minima epochs.

Development of a VLF receiver based on Red Pitaya for space weather studies

A new VLF (Very low Frequency) receiver has been developed by the Peruvian Space Agency (CONIDA) for space weather studies. The receiver has been designed based on a Red Pitaya board which performs an SDR (Software Defined Radio) to digitize, process and store the signal. The receiver is composed of a vertical antenna, a preamplifier to filter and amplify the incoming VLF signals from several transmitters located around the world. The receiver is able to cover a bandwidth from 1 up to 50 kHz and it has been developed in such a way as to be cost-effective, autonomous and solar-powered, making it suitable for installation in multiple locations with different geographic conditions. We show the performance of the receiver, the typical daily pattern of the lower ionosphere for the NAA VLF signal, as observed in Peru, and the first solar flares observed. The VLF amplitude curves recorded are validated by comparing them with data from SAVNET (The South American VLF Network) receiver installed in Peru. In a first effort to investigate the impact of solar flares on the lower ionosphere, we conducted a statistical analysis between VLF amplitude perturbations and 1–8 Å solar X-rays flux provided by GOES satellites, resulting in a linear relationship.

Emission Line Intensity Ratios of Fe xxvi/ xxv/ xxiv in Solar Flares Observed by Hinotori

High-resolution spectra observed by the Solar X-ray spectrometer on board the Hinotori mission are revisited. Flat crystals slightly offset to the satellite spin axis produce automatic spectral scans for emission lines emerging from highly charged iron ions in solar flares every half-spin time period. All the downlinked data of the mission are converted to FITS format and major flare spectral data are revived as IDL save files in ISAS/DARTS. Based on these data sets, single-temperature fits are performed for the emission line complex of highly charged iron ions in the wavelength range of 1.75–1.95 Å and compared with theoretical predictions. Synthetic spectra with single electron temperatures estimated from j/w line-intensity ratios fit fairly well for Fe xxiv and Fe xxiii lines in the wavelength range of 1.85–1.88 Å, while intensity ratios of Fe xxv lines (x, y, z) and the inner-shell excitation line of Fe xxiv (q) to the Fe xxv resonance line (w) have systematic excesses. Empirical relations for the observed line ratios are derived. Ion fractions of Fe+25/Fe+24 estimated by intensity ratios of Lyα/w in the temperature range of log T e =7.25–7.45 are consistent with values in ionization equilibrium, and the remaining excesses of the Fe xxv line ratios may suggest problems with the atomic parameters or atomic modeling.