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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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CONFINED FLARES IN SOLAR ACTIVE REGION 12192 FROM 2014 OCTOBER 18 TO 29
摘要： Using the observations from the Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory, we investigate 6 X-class and 29 M-class ?ares occurring in solar active region (AR) 12192 from October 18 to 29. Among them, 30 (including 6 X- and 24 M-class) ?ares originated from the AR core, and the other 5 M-?ares appeared at the AR periphery. Four of the X-?ares exhibited similar ?aring structures, indicating they were homologous ?ares with an analogous triggering mechanism. The possible scenario is that photospheric motions of emerged magnetic ?uxes lead to shearing of the associated coronal magnetic ?eld, which then yields a tether-cutting favorable con?guration. Among the ?ve periphery M-?ares, four were associated with jet activities. The HMI vertical magnetic ?eld data show that the photospheric ?uxes of opposite magnetic polarities emerged, converged, and canceled with each other at the footpoints of the jets before the ?ares. Only one M-?are from the AR periphery was followed by a coronal mass ejection (CME). From October 20 to 26, the mean decay index of the horizontal background ?eld within the height range of 40–105 Mm is below the typical threshold for torus instability onset. This suggests that a strong con?nement from the overlying magnetic ?eld might be responsible for the poor CME production of AR 12192.
关键词： Sun: coronal mass ejections (CMEs),Sun: ?ares,Sun: activity,Sun: UV radiation
更新于2025-09-23 15:22:29
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Lost and found sunquake in the 6 September 2011 flare caused by beam electrons
摘要： The active region NOAA 11283 produced two X-class ?ares on 6 and 7 September 2011 that have been well studied by many authors. The X2.1 class ?are occurred on September 6, 2011 and was associated with the ?rst of two homologous white light ?ares produced by this region, but no sunquake was found with it despite the one being detected in the second ?are of 7 September 2011. In this paper we present the ?rst observation of a sunquake for the 6 September 2011 ?are detected via statistical signi?cance analysis of egression power and veri?ed via directional holography and time–distance diagram. The surface wavefront exhibits directional preference in the north-west direction We interpret this sunquake and the associated ?are emission with a combination of a radiative hydrodynamic model of a ?aring atmosphere heated by electron beam and a hydrodynamic model of acoustic wave generation in the solar interior generated by a supersonic shock. The hydrodynamic model of the ?aring atmosphere produces a hydrodynamic shock travelling with supersonic velocities toward the photosphere and beneath. For the ?rst time we derive velocities (up to 140 km s?1) and onset time (about 50 s after ?are onset) of the shock deposition at given depths of the interior. The shock parameters are con?rmed by the radiative signatures in hard X-rays and white light emission observed from this ?are. The shock propagation in the interior beneath the ?are is found to generate acoustic waves elongated in the direction of shock propagation, that results in an anisotropic wavefront seen on the solar surface. Matching the detected seismic signatures on the solar surface with the acoustic wave front model derived for the simulated shock velocities, we infer that the shock has to be deposited under an angle of about 30? to the local solar vertical. Hence, the improved seismic detection technique combined with the double hydrodynamic model reported in this study opens new perspectives for observation and interpretation of seismic signatures in solar ?ares.
关键词： Sun: X-rays, gamma rays,radiative transfer,Sun: ?ares,Sun: helioseismology,hydrodynamics
更新于2025-09-23 15:21:21
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First Detection of Solar Flare Emission in Mid-ultraviolet Balmer Continuum
摘要： We present the ?rst detection of solar ?are emission at mid-ultraviolet wavelengths around 2000?? by the channel 2 of the Large-Yield RAdiometer (LYRA) on board the PRoject for OnBoard Autonomy 2 mission. The ?are (SOL20170906) was also observed in the channel 1 of LYRA centered at the H I Lyα line at 1216??, showing a clear non-thermal pro?le in both channels. The ?are radiation in channel 2 is consistent with the hydrogen Balmer continuum emission produced by an optically thin chromospheric slab heated up to 10,000 K. Simultaneous observations in channels 1 and 2 allow the separation of the line emission (primarily from the Lyα line) from the Balmer continuum emission. Together with the recent detection of the Balmer continuum emission in the near-ultraviolet by the Interface Region Imaging Spectrometer, the LYRA observations strengthen the interpretation of broadband ?are emission as the hydrogen recombination continua originating in the chromosphere.
关键词： Sun: ?ares,Sun: chromosphere,Sun: UV radiation
更新于2025-09-23 15:21:01
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Solar jet-like features rooted in flare ribbons
摘要： Employing the high spatio-temporal Interface Region Imaging Spectrograph 1330 ?A observations, we investigated the jet-like features that occurred during the X8.2 class ?are in NOAA active region (AR) 12673 on 2017 September 10. These jet-like features were rooted in the ?are ribbons. We examined 15 features, and the mean values of the lifetimes, projected widths, lengths, and velocities of these features were 87 s, 890 km, 2.7 Mm, and 70 km s?1, respectively. We also observed many jet-like features which happened during the X1.0 class ?are on 2014 October 25. We studied the spectra at the base of a jet-like feature during its development. The Fe XXI 1354.08 ?A line in the corona displays blueshift, while the Si IV 1402.77 ?A line in the transition region exhibits redshift, which indicates the chromospheric evaporation. This is the ?rst time that the jet-like features are reported to be rooted in the ?are ribbons, and we suggest that these jet-like features were driven by the mechanism of chromospheric evaporation.
关键词： Sun: atmosphere,Sun: ?ares,Sun: evolution,Sun: activity
更新于2025-09-19 17:15:36
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Direct observation of the energy release site in a solar flare by SDO/AIA, Hinode/EIS, and RHESSI
摘要： the detection of Aims. We present direct evidence of the main energy release site in a non-eruptive solar ?are, SOL2013-11-09T06:38 UT. This GOES class C2.6 event was characterised by two ?aring ribbons and a compact, bright coronal source located between them, which is the focus of our study. Methods. We use imaging from SDO/AIA, and imaging spectroscopy from RHESSI to characterise the thermal and non-thermal emission from the coronal source, and EUV spectroscopy from the Hinode/Extreme ultraviolet Imaging Spectrometer, which scanned the coronal source during the impulsive peak, to analyse Doppler shifts in Fe xii (log T = 6.2) and Fe xxiv (log T = 7.2) emission lines, and determine the source density. Results. The coronal source exhibited an impulsive emission lightcurve in all SDO/AIA ?lters during the impulsive phase. RHESSI hard X-ray images indicate both thermal and non-thermal emission at the coronal source, and its plasma temperature derived from RHESSI imaging spectroscopy shows an impulsive rise, reaching a maximum at 12–13 MK about 10 s prior to the hard X-ray peak. High red-shifts associated with this bright source indicate down?ows of 40–250 km s?1 at a broad range of temperatures, interpreted as loop shrinkage and/or out?ows along the magnetic ?eld. Out?ows from the coronal source towards each ribbon are also observed by SDO/AIA images at 171, 193, 211, 304, and 1600 ?. The electron density of the source obtained from a Fe xiv line pair is 1011.50 cm?3 which is collisionally thick to electrons with energy up to 45–65 keV, responsible for the source’s non-thermal X-ray emission. Conclusions. Given the rich observational evidence, we conclude that the bright coronal source is the location of the main release of magnetic energy in this ?are, with a geometry consistent with component reconnection between crossing, current-carrying loops. We argue that the energy that can be released via reconnection, based on observational estimates, can plausibly account for the non-thermal energetics of the ?are.
关键词： Sun: UV radiation,Sun: ?ares,line: pro?les,magnetic reconnection,Sun: corona,Sun: X-rays, gamma rays
更新于2025-09-10 09:29:36
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H <i>α</i> spectroscopy and multiwavelength imaging of a solar flare caused by filament eruption
摘要： Context. We study a sequence of eruptive events including ?lament eruption, a GOES C4.3 ?are, and a coronal mass ejection. Aims. We aim to identify the possible trigger(s) and precursor(s) of the ?lament destabilisation, investigate ?are kernel characteristics, ?are ribbons/kernels formation and evolution, study the interrelation of the ?lament-eruption/?are/coronal-mass-ejection phenomena as part of the integral active-region magnetic ?eld con?guration, and determine Hα line pro?le evolution during the eruptive phenomena. Methods. Multi-instrument observations are analysed including Hα line pro?les, speckle images at Hα – 0.8 ? and Hα + 0.8 ? from IBIS at DST/NSO, EUV images and magnetograms from the SDO, coronagraph images from STEREO, and the X-ray ?ux observations from Fermi and GOES. Results. We establish that the ?lament destabilisation and eruption are the main triggers for the ?aring activity. A surge-like event with a circular ribbon in one of the ?lament footpoints is determined as the possible trigger of the ?lament destabilisation. Plasma draining in this footpoint is identi?ed as the precursor for the ?lament eruption. A magnetic ?ux emergence prior to the ?lament destabilisation followed by a high rate of ?ux cancellation of 1.34 × 1016 Mx s?1 is found during the ?are activity. The ?are X-ray lightcurves reveal three phases that are found to be associated with three di?erent ribbons occurring consecutively. A kernel from each ribbon is selected and analysed. The kernel lightcurves and Hα line pro?les reveal that the emission increase in the line centre is stronger than that in the line wings. A delay of around 5–6 min is found between the increase in the line centre and the occurrence of red asymmetry. Only red asymmetry is observed in the ribbons during the impulsive phases. Blue asymmetry is only associated with the dynamic ?lament.
关键词： Sun: activity,Sun: ?ares,line: pro?les,Sun: ?laments,prominences
更新于2025-09-10 09:29:36
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Measurement of vector magnetic field in a flare kernel with a spectropolarimetric observation in He ?i 10830??
摘要： A ?are kernel associated with a C4 class ?are was observed in a spectral window including the He I triplet 10830 ?A and Si I 10827 ?A with a spectropolarimeter on the Domeless Solar Telescope at Hida Observatory on 2015 August 9. The observed Stokes pro?les of the He I triplet in the ?are kernel in its post-maximum phase are well reproduced through inversions considering the Zeeman and the Paschen–Back effects with a three-slab model of the ?are kernel, in which two slabs which have upward and downward velocities produce emissions and one slab produces an absorption. The magnetic ?eld strength inferred from the emission components of the He I line is 1400 G, which is signi?cantly stronger than 690 G that is observed at the same location in the same line 6.5 hr before the ?are. In addition, the photospheric magnetic ?eld vector derived from the Si I10827 ?A is similar to that of the ?are kernel. To explain this result, we suggest that the emission in the He I triplet during the ?are is produced in the deep layer, around which bombardment of non-thermal electrons leads to the formation of a coronal temperature plasma. Assuming a hydrogen column density at the location where the He I emissions are formed, and a power-law index of non-thermal electron energy distribution, we derived the low-energy cuto? of the non-thermal electron as 20–30 keV, which is consistent with that inferred from hard X-ray data obtained by RHESSI.
关键词： Sun: ?ares,Sun: magnetic ?elds,Sun: chromosphere,polarization
更新于2025-09-10 09:29:36
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Oscillations Accompanying a He?i 10830 ? Negative Flare in a Solar Facula
摘要： On 21 September 2012, we carried out spectral observations of a solar facula in the Si I 10827 ?, He I 10830 ?, and Hα spectral lines. Later, in the process of analyzing the data, we found a small-scale ?are in the middle of the time series. Based on the anomalous increase in the absorption of the He I 10830 ? line, we identi?ed this ?are as a negative ?are. The aim of this article is to study the in?uence of the negative ?are on the oscillation characteristics in the facular photosphere and chromosphere. We measured the line-of-sight (LOS) velocity and intensity of all the three lines as well as the half-width of the chromospheric lines. We also used the Helioseismic and Magnetic Imager (HMI) magnetic ?eld data. The ?are caused a modulation of all these parameters. In the location of the negative ?are, the amplitude of the oscillations increased four times on average. In the adjacent magnetic ?eld local maxima, the chromospheric LOS velocity oscillations appreciably decreased during the ?are. The facular region oscillated as a whole with a 5-minute period before the ?are, and this synchronicity was disrupted after the ?are. The ?are changed the spectral composition of the LOS magnetic ?eld oscillations, causing an increase in the low-frequency oscillation power.
关键词： Sun: faculae, plages,Sun: oscillations,Sun: ?ares
更新于2025-09-09 09:28:46
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Frequency rising sub-THz emission from solar flare ribbons
摘要： Observations of solar ?ares at sub-THz frequencies (millimetre and sub-millimetre wavelengths) over the last two decades often show a spectral component rising with frequency. Unlike a typical gyrosynchrotron spectrum decreasing with frequency or a weak thermal component from hot coronal plasma, the observations can demonstrate a high ?ux level (up to ～104 solar ?ux units at 0.4 THz) and fast variability on sub-second timescales. Although, many models have been put forward to explain the puzzling observations, none of them has clear observational support. Here we propose a scenario to explain the intriguing sub-THz observations. We show that the model, based on free-free emission from the plasma of ?are ribbons at temperatures 104?106 K, is consistent with all existing observations of frequency-rising sub-THz ?are emission. The model provides a temperature diagnostic of the ?aring chromosphere and suggests fast heating and cooling of the dense transition region plasma.
关键词： Sun: ?ares,Sun: radio radiation,Sun: activity,Sun: chromosphere,Sun: magnetic ?elds,Sun: X-rays, gamma rays
更新于2025-09-04 15:30:14