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Determination of Differential Emission Measure from Solar Extreme Ultraviolet Images
摘要： The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) has been providing high-cadence, high-resolution, full-disk UV-visible/extreme ultraviolet (EUV) images since 2010, with the best time coverage among all the solar missions. A number of codes have been developed to extract plasma differential emission measures (DEMs) from AIA images. Although widely used, they cannot effectively constrain the DEM at ?aring temperatures with AIA data alone. This often results in much higher X-ray ?uxes than observed. One way to solve the problem is by adding more constraint from other data sets (such as soft X-ray images and ?uxes). However, the spatial information of plasma DEMs are lost in many cases. In this Letter, we present a different approach to constrain the DEMs. We tested the sparse inversion code and show that the default settings reproduce X-ray ?uxes that could be too high. Based on the tests with both simulated and observed AIA data, we provided recommended settings of basis functions and tolerances. The new DEM solutions derived from AIA images alone are much more consistent with (thermal) X-ray observations, and provide valuable information by mapping the thermal plasma from ～0.3 to ～30 MK. Such improvement is a key step in understanding the nature of individual X-ray sources, and particularly important for studies of ?are initiation.
关键词： magnetic reconnection,methods: data analysis,Sun: X-rays, gamma rays,Sun: ?ares,Sun: corona,Sun: UV radiation
更新于2025-09-23 15:23:52
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Thermal structure of a hot non-flaring corona from Hinode/EIS
摘要： Aims. In previous studies, a very hot plasma component has been diagnosed in solar active regions through the images in three different narrow-band channels of Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). This diagnostic from extreme ultraviolet (EUV) imaging data has also been supported by the matching morphology of emission in the hot Ca XVII line, as observed with Extreme-Ultraviolet Imaging Spectrometer (EIS) on board Hinode. This evidence is debated because of the unknown distribution of the emission measure along the line of sight. Here we investigate in detail the thermal distribution of one such region using EUV spectroscopic data. Methods. In an active region observed with SDO/AIA, Hinode/EIS, and X-ray telescope (XRT), we select a sub-region with a very hot plasma component and another cooler sub-region for comparison. The average spectrum is extracted for both, and 14 intense lines are selected for analysis that probe the 5.5 < log T < 7 temperature range uniformly. From these lines, the emission measure distributions are reconstructed with the Markov-chain Monte Carlo method. Results are cross-checked in comparison with the two sub-regions, with a different inversion method, with the morphology of the images, and with the addition of fluxes measured with narrow, and broadband imagers. Results. We find that, whereas the cool region has a flat and featureless distribution that drops at temperature log T ≥ 6.3, the distribution of the hot region shows a well-defined peak at log T = 6.6 and gradually decreasing trends on both sides, thus supporting the very hot nature of the hot component diagnosed with imagers. The other cross-checks are consistent with this result. Conclusions. This study provides a completion of the analysis of active region components, and the resulting scenario supports the presence of a minor very hot plasma component in the core, with temperatures log T > 6.6.
关键词： techniques: imaging spectroscopy,Sun: UV radiation,Sun: corona,techniques: spectroscopic,Sun: X-rays, gamma rays
更新于2025-09-23 15:23:52
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Blobs in recurring extreme-ultraviolet jets
摘要： Context. Coronal jets are one type of ubiquitous small-scale activity that is caused by magnetic reconnection in the solar corona. They are often associated with cool surges in the chromosphere. Aims. In this paper, we report our discovery of blobs in the recurrent and homologous jets that occurred at the western edge of the NOAA active region 11259 on 2011 July 22. Methods. The jets were observed in the seven extreme-ultraviolet (EUV) ?lters of the Atmospheric Imaging Assembly instrument aboard the Solar Dynamics Observatory. Using the base-di?erence images of the six ?lters (94, 131, 171, 211, 193, and 335 ?), we carried out the di?erential emission measure (DEM) analyses to explore the thermodynamic evolutions of the jets. The jets were accompanied by cool surges observed in the Hα line center of the ground-based telescope in the Big Bear Solar Observatory. Results. The jets that had lifetimes of 20?30 min recurred at the same place for three times with an interval of 40?45 min. Interestingly, each of the jets intermittently experienced several upward eruptions at the speed of 120?450 km s?1. After reaching the maximum heights, they returned back to the solar surface, showing near-parabolic trajectories. The falling phases were more evident in the low-T ?lters than in the high-T ?lters, indicating that the jets experienced cooling after the onset of eruptions. We identi?ed bright and compact blobs in the jets during their rising phases. The simultaneous presence of blobs in all the EUV ?lters were consistent with the broad ranges of the DEM pro?les of the blobs (5.5 ≤ log T ≤ 7.5), indicating their multi-thermal nature. The median temperatures of the blobs were ～2.3 MK. The blobs that were ～3 Mm in diameter had lifetimes of 24?60 s. Conclusions. To our knowledge, this is the ?rst report of blobs in coronal jets. We propose that these blobs are plasmoids created by the magnetic reconnection as a result of tearing-mode instability and are ejected out along the jets.
关键词： Sun: chromosphere,Sun: corona,Sun: activity
更新于2025-09-23 15:23:52
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A Quasi-periodic Propagating Wave and Extreme-ultraviolet Waves Excited Simultaneously in a Solar Eruption Event
摘要： Quasi-periodic fast-propagating (QFP) magnetosonic waves and extreme-ultraviolet (EUV) waves were proposed to be driven by solar flares and coronal mass ejections (CMEs), respectively. In this Letter, we present a detailed analysis of an interesting event in which we find that both QFP magnetosonic waves and EUV waves are excited simultaneously in one solar eruption event. The co-existence of the two wave phenomena offers an excellent opportunity to explore their driving mechanisms. The QFP waves propagate in a funnel-like loop system with a speed of 682–837 km s-1 and a lifetime of 2 minutes. On the contrary, the EUV waves, which present a faster component and a slower component, propagate in a wide angular extent, experiencing reflection and refraction across a magnetic quasi-separatrix layer. The faster component of the EUV waves travels with a speed of 412–1287 km s-1, whereas the slower component travels with a speed of 246–390 km s-1. The lifetime of the EUV waves is ～15 minutes. It is revealed that the faster component of the EUV waves is cospatial with the first wavefront of the QFP wave train. The QFP waves have a period of about 45 ± 5 s, which is absent in the associated flares. All of these results imply that QFP waves can also be excited by mass ejections, including CMEs or jets.
关键词： Sun: oscillations,waves,Sun: flares,Sun: corona,Sun: magnetic fields
更新于2025-09-23 15:22:29
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Magnetic Loops above a Small Flux-emerging Region Observed by <i>IRIS</i> , <i>Hinode</i> , and <i>SDO</i>
摘要： I report on observations of a set of magnetic loops above a region with late-phase ?ux emergence taken by IRIS, Hinode, and SDO. The loop system consists of many transition-region loop threads that are 5″–12″ in length and ～0 5 in width and coronal loops with similar length and ～2″ width. Although the loop system consists of threads with different temperatures, most individual loop threads have temperatures in a narrow range. In the middle of the loop system, there is a clear systematic blueshift of about 10 km s?1 in the transition region that is consistent with a ?ux-emerging picture, while a redshift of about 10 km s?1 in the corona is observed. The nonthermal velocity of the loop system is smaller than that of the surrounding region in the transition region but is comparable that in the corona. The electron densities of the coronal counterpart of the loop system range from 1×109 cm?3 to 4×109 cm?3. The electron density of a transition-region loop is also measured and found to be about 5×1010 cm?3, a magnitude larger than that in the coronal loops. In agreement with imaging data, the temperature pro?les derived from the differential emission measurement technique con?rm that some of the loops have been heated to corona level. Our observations indicate that the ?ux emergence in its late phase is much different from that at the early stage. While the observed transition region is dominated by emerging ?ux, these emerging loops could be heated to corona level, and the heating (if via nonthermal processes) most likely takes place only after they reach the transition region or lower corona.
关键词： Sun: atmosphere,Sun: transition region,Sun: corona
更新于2025-09-23 15:22:29
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Response of Hinode XRT to quiet Sun, active region and flare plasma
摘要： Aims. We examine the response of the Hinode X-Ray Telescope (XRT), using simultaneous observations with the Hinode Extreme-ultraviolet Imaging Spectrometer (EIS), for a flare, an active region and a quiet Sun region. We also examine the relative intensity calibration of EIS and XRT. Methods. EIS differential emission measure distribution (DEM) curves were used to create synthetic spectra with the CHIANTI atomic database. The contribution of spectral lines and continuum emission to each of the XRT channels was determined from the synthetic spectra, which were then convolved with the effective area of each XRT channel. The predicted total count rates for each channel were compared with the observed count rates. The effects of varying elemental abundances and the temperature range for the inversion were investigated. DEMs obtained from the XRT bands were also computed and compared to those obtained with EIS. Results. For the active region observations, the observed XRT count rates for most of the channels are in reasonable agreement with those predicted using EIS observations, but are dependent on the elemental abundances chosen. Significant discrepancies between predicted and observed count rates were found and are discussed for the adjacent quiet Sun region and also for the flare. Synthetic spectra and continuum emission contributing to the XRT channels are presented and discussed for the active region, quiet Sun and flare observations.
关键词： Sun: abundances,gamma rays,Sun: corona,Sun: X-rays
更新于2025-09-23 15:22:29
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Characterization of the White-light Brightness of the F-corona between 5° and 24° Elongation
摘要： The white-light F-corona arises from light scattered by circumsolar dust. Using weekly models of the eastern side of the F-corona between 5° and 24° elongation, we analyzed the elongation and time dependence of the brightness of its photometric axis. The models were constructed from STEREO-A SECCHI/HI-1 images taken between 2007 December and 2014 March. We found that the brightness profiles can be approximated by power laws, with the coefficients of the models depending upon the observer’s ecliptic longitude. Their variation is not symmetric with respect to the orbital nodes of the dust plane, nor is the behavior similar in the two halves of the spacecraft orbit delimited by the line of nodes. The exponents range between ?2.31 and ?2.35, the former occurring when the observer is at the nodes. The asymmetry observed in the behavior of the proportionality constant is indicative of the projected center of the dust cloud being offset from the Sun’s center by ～0.4 Re. The coefficients exhibit a secular variation correlated with the location of the barycenter of the solar system. We also used the HI-1 frames obtained during STEREO-A calibration rolls to model the 360° F-corona. We found that (1) its flattening index (f = 1 - Rpol/Req) decreases from ～0.66 to ～0.46 with decreasing elongation and (2) the isophotes’ shape can be approximated by a series of superellipses, with the superellipse index n increasing (nonlinearly) with brightness (n ~ 1.65). Cubic extrapolation of the results below 5° elongation points to a circular F-corona below ～1° elongation.
关键词： scattering,zodiacal dust,methods: data analysis,Sun: corona,techniques: image processing
更新于2025-09-23 15:22:29
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A swirling flare-related EUV jet
摘要： Aims. We report our observations of a swirling flare-related extreme-ultraviolet (EUV) jet on 2011 October 15 at the edge of NOAA active region 11314. Methods. We used the multiwavelength observations in the EUV passbands from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO). We extracted a wide slit along the jet axis and 12 thin slits across its axis to investigate the longitudinal motion and transverse rotation. We also used data from the Extreme-Ultraviolet Imager (EUVI) aboard the Solar TErrestrial RElations Observatory (STEREO) spacecraft to investigate the three-dimensional (3D) structure of the jet. Ground-based Hα images from the El Teide Observatory, a member of the Global Oscillation Network Group (GONG), provide a good opportunity to explore the relationship between the cool surge and the hot jet. Line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) aboard SDO enable us to study the magnetic evolution of the flare/jet event. We carried out potential-field extrapolation to calculate the magnetic configuration associated with the jet. Results. The onset of jet eruption coincided with the start time of the C1.6 flare impulsive phase. The initial velocity and acceleration of the longitudinal motion were 254 ± 10 km s?1 and ?97 ± 5 m s?2, respectively. The jet presented helical structure and transverse swirling motion at the beginning of its eruption. The counter-clockwise rotation slowed down from an average velocity of ～122 km s?1 to ～80 km s?1. The interwinding thick threads of the jet untwisted into multiple thin threads during the rotation that lasted for one cycle with a period of ～7 min and an amplitude that increases from ～3.2 Mm at the bottom to ～11 Mm at the upper part. Afterwards, the curtain-like leading edge of the jet continued rising without rotation, leaving a dimming region behind, before falling back to the solar surface. The appearance/disappearance of dimming corresponded to the longitudinal ascending/descending motions of jet. Cospatial Hα surge and EUV dimming imply that the dimming resulted from the absorption of hot EUV emission by the cool surge. The flare/jet event was caused by continuous magnetic cancellation before the start of the flare. The jet was associated with the open magnetic fields at the edge of AR 11314.
关键词： Sun: corona,Sun: oscillations,Sun: flares
更新于2025-09-23 15:21:21
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Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona
摘要： A component of space weather, electron beams are routinely accelerated in the solar atmosphere and propagate through interplanetary space. Electron beams interact with Langmuir waves resulting in type III radio bursts. They expand along the trajectory and, using kinetic simulations, we explore the expansion as the electrons propagate away from the Sun. Specifically, we investigate the front, peak, and back of the electron beam in space from derived radio brightness temperatures of fundamental type III emission. The front of the electron beam travels at speeds from 0.2c to 0.7c, significantly faster than the back of the beam, which travels at speeds between 0.12c and 0.35c. The difference in speed between the front and the back elongates the electron beam in time. The rate of beam elongation has a 0.98 correlation coefficient with the peak velocity, in line with predictions from type III observations. The inferred speeds of electron beams initially increase close to the acceleration region and then decrease through the solar corona. Larger starting densities and harder initial spectral indices result in longer and faster type III sources. Faster electron beams have higher beam energy densities, and produce type IIIs with higher peak brightness temperatures and shorter FWHM durations. Higher background plasma temperatures also increase speed, particularly at the back of the beam. We show how our predictions of electron beam evolution influences type III bandwidth and drift rates. Our radial predictions of electron beam speed and expansion can be tested by the upcoming in situ electron beam measurements made by Solar Orbiter and Parker Solar Probe.
关键词： Sun: corona,Sun: particle emission,Sun: flares,Sun: radio radiation,solar wind
更新于2025-09-23 15:21:01
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Structural properties of the solar flare-producing coronal current system developed in an emerging magnetic flux tube
摘要： The activity of a magnetic structure formed in the solar corona depends on a coronal current system developed in the structure, which determines how an electric current flows in the corona. To investigate structural properties of the coronal current system responsible for producing a solar flare, we perform magnetohydrodynamic simulation of an emerging magnetic flux tube which forms a coronal magnetic structure. Investigation using fractal dimensional analysis and electric current streamlines reveals that the flare-producing coronal current system relies on a specific coronal current structure of two-dimensional spatiality, which has a sub-region where a nearly anti-parallel magnetic field configuration is spontaneously generated. We discuss the role of this locally generated anti-parallel magnetic field configuration in causing the reconnection of a three-dimensional magnetic field, which is a possible mechanism for producing a flare. We also discuss how the twist of a magnetic flux tube affects structural properties of a coronal current system, showing how much volume current flux is carried into the corona by an emerging flux tube. This gives a way to evaluate the activity of a coronal magnetic structure.
关键词： magnetohydrodynamics (MHD),Sun: magnetic fields,Sun: corona,methods: numerical,Sun: flares
更新于2025-09-23 15:21:01