Thermodynamic and magnetic evolution of an eruptive C-class solar flare observed with SST/TRIPPEL-SP

A 20 s cadence Transiting Exoplanet Survey Satellite monitoring campaign of 226 low-mass flare stars during Cycle 3 recorded 3792 stellar flares of ≥1032 erg. We explore the time-resolved emission and substructure in 440 of the largest flares observed at high signal-to-noise, 97% of which released energies of ≥1033 erg. We discover degeneracy present at 2 minute cadence between sharply peaked and weakly peaked flares is common, although 20 s cadence breaks these degeneracies. We better resolve the rise phases and find 46% of large flares exhibit substructure during the rise phase. We observe 49 candidate quasi-periodic pulsations (QPP) and confirm 17 at ≥3σ. Most of our QPPs have periods less than 10 minutes, suggesting short-period optical QPPs are common. We find QPPs in both the rise and decay phases of flares, including a rise-phase QPP in a large flare from Proxima Cen. We confirm that the Davenport et al. template provides a good fit to most classical flares observed at high cadence, although 9% favor Gaussian peaks instead. We characterize the properties of complex flares, finding 17% of complex flares exhibit “peak-bump” morphologies composed of a large, highly impulsive peak followed by a second, more gradual Gaussian peak. We also estimate the UVC surface fluences of temperate planets at flare peak and find one-third of 1034 erg flares reach the D90 dose of Deinococcus radiodurans in just 20 s in the absence of an atmosphere.

Solar Physics Solar flares are bright flashes and associated eruptions of plasma from the Sun that are thought to be powered by violent rearrangement of the magnetic fields near sunspots. Fleishman et al. observed a bright solar flare with a microwave interferometer, allowing them to map the magnetic field in the solar corona and monitor how it changed during the flare. They found a large drop in the local field strength over 2 minutes, releasing enough magnetic energy to power the entire solar flare. Determining the origin of this energy will help to predict how strong future solar flares may be and their potential space weather impacts on Earth. Science , this issue p. [278][1] [1]: /lookup/doi/10.1126/science.aax6874

Context. Quiet-Sun Ellerman bombs (QSEBs) are small-scale magnetic reconnection events in the lower atmosphere of the quiet Sun. Recent work has shown that a small percentage of them can occur co-spatially and co-temporally with ultraviolet (UV) brightenings in the transition region. Aims. We aim to understand how the magnetic topologies associated with closely occurring QSEBs and UV brightenings can facilitate energy transport and connect these events. Methods. We used high-resolution Hβ observations from the Swedish 1-m Solar Telescope (SST) and detected QSEBs using k-means clustering. We obtained the magnetic field topology from potential field extrapolations using spectro-polarimetric data in the photospheric Fe I 6173 Å line. To detect UV brightenings, we used coordinated and co-aligned data from the Interface Region Imaging Spectrograph (IRIS) and imposed a threshold of 5σ above the median background on the (IRIS) 1400 Å slit-jaw image channel. Results. We identify four distinct magnetic configurations that associate QSEBs with UV brightenings, including a simple dipole configuration and more complex fan-spine topologies with a 3D magnetic null point. In the fan-spine topology, the UV brightenings occur near the 3D null point, while QSEBs can be found close to the footpoints of the outer spine, the inner spine, and the fan surface. The height of the 3D null varies between 0.2 Mm and 2.6 Mm, depending on the magnetic field strength in the region. Some QSEBs and UV brightenings, though occurring close to each other, are not topologically connected with the same reconnection process. The energy released during QSEBs falls in the range 1023–1024 ergs. Conclusions. This study shows that magnetic connectivity and topological features, such as 3D null points, are crucial in linking QSEBs in the lower atmosphere with UV brightenings in the transition region.

Aims. We model the atmosphere of the ultra-hot Jupiter (UHJ) WASP-178b while accounting for non-local thermodynamical equilibrium (NLTE) effects and compare synthetic transmission spectra with near-ultraviolet (NUV) and optical observations. Methods. We used the HELIOS code (LTE) in the lower atmosphere and the ClOUDY code (LTE or NLTE) in the middle and upper atmosphere to compute the temperature-pressure (TP) and abundance profiles. We further used CLOUDY to compute the theoretical planetary transmission spectrum both in LTE and NLTE for comparison with observations. Results. We find an isothermal TP profile at pressures higher than 10 mbar and lower than 10−8 bar, with an almost linear increase from ∼2200 K to ∼8100 K in between. The temperature structure is driven by NLTE effects, particularly in the form of increased heating resulting from the overpopulation of long-lived FeII levels with strong transitions in the NUV band, where the stellar emission is strong, and of decreased cooling due to the underpopulation of MgI and MgII levels that dominate the cooling. The planetary atmosphere is hydrostatic up to pressures of ∼1 nbar, and thus accurately modelling spectral lines forming at pressures lower than ∼1 nbar requires accounting for both hydrodynamics and NLTE effects. The NLTE synthetic transmission spectrum overestimates the observed Hα and Hβ absorption, while the LTE model is in good agreement, which is surprising because the opposite has been found for the other UHJs for which NLTE modelling has been performed. In the NUV, we find an excellent match between the NLTE transmission spectrum and the HST/UVIS data, contrary to the LTE model. This contrasts with previous LTE results requiring SiO absorption to fit the observations. Conclusions. The accurate characterisation of the atmosphere of UHJs is possible only when accounting for NLTE effects and particularly for the level population of Fe and Mg, which respectively dominate heating and cooling.

Context. The diagnostics of stellar flaring coronal loops have been so far largely based on the analysis of the decay phase. Aims. We derive new diagnostics from the analysis of the rise and peak phase of stellar flares. Methods. We release the assumption of full equilibrium of the flaring loop at the flare peak, according to the frequently observed delay between the temperature and the density maximum. From scaling laws and hydrodynamic simulations we derive diagnostic formulas as a function of observable quantities and times. Results. We obtain a diagnostic toolset related to the rise phase, including the loop length, density and aspect ratio. We discuss the limitations of this approach and find that the assumption of loop equilibrium in the analysis of the decay leads to a moderate overestimate of the loop length. A few relevant applications to previously analyzed stellar flares are shown. Conclusions. The analysis of the flare rise and peak phase complements and completes the analysis of the decay phase.

Activities on the Sun’s surface can produce dynamic conditions in the Earth’s outer space environment, which can affect the Earth, space-borne and ground-based technologies, including Global Navigation Satellite Systems (GNSS). Delay of GNSS signal can occur during its propagation through the upper Earth’s atmosphere—the ionosphere, representing the major limitation in GNSS positioning applications. In this paper, high level of solar activity and intense bursts of radiation from the release of magnetic energy on the Sun, known as solar flares, are studied. The investigation covers the detection of events on the Sun’s surface, conditions in near-Earth’s space environment, geomagnetic field, ionosphere and GNSS positioning estimates. In October 2014, more than 200 solar flares were detected and about a quarter of total amount belonged to solar flares of M and X class. Impact on ionospheric layers is studied: D layer with SuperSID (sudden ionospheric disturbances) monitor and electron density to F2 layer with GNSS-derived total electron content. Used GNSS stations belong to EUREF Permanent Network (EPN) in Bosnia and Herzegovina and Croatia. Precise Point Positioning is performed in the Bernese GNSS Software. Solar radio emissions were high in the second half of the month, when more M and X solar flares occurred. Ionospheric electron density was enhanced, reaching its peak during the high level of solar activity and the period of strongest solar flares occurrence, while position estimates show higher deviations from the EPN weekly solution in Up component (at least for two times). Higher-order ionospheric terms remained after applying the L3 ionosphere-free solution, which should be taken into account in precise positioning during increased level of solar activity.

The studies were carried out preliminary within the framework of the RSF project 15-19-20013 Creation of an adaptive system ensuring operation of a large-sized solar telescope under conditions of strong atmospheric turbulence. It is known that the use of adaptive optics (AO) systems is the most radical way for reducing the effect of atmospheric distortions. AO systems correct distortions introduced by the Earth's atmosphere into the image of a space object in real time. The creation of an AO system for large-aperture solar telescopes still is a scientific and engineering challenge. Currently, for the largest Russian solar telescopes, in particular, the Large Solar Vacuum Telescope (LSVT), the Automated Solar Telescope (AST) and the 3-meter Large Solar Telescope (LST) under development, promising new- generation systems are being developed and implemented based on the principles of multi-mirror adaptive correction.

view Abstract Citations (119) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-resolution X-ray spectra of solar flares. IV - General spectral properties of M type flares Feldman, U. ; Doschek, G. A. ; Kreplin, R. W. ; Mariska, J. T. Abstract The spectral characteristics in selected narrow regions of the X-ray spectrum of class M solar flares are analyzed. High-resolution spectra in the ranges 1.82-1.97, 2.98-3.07, 3.14-3.24 and 8.26-8.53 A, which contain lines important for the determination of electron temperature and departure from ionization equilibrium, were recorded by spaceborne Bragg crystal spectrometers. Temperatures of up to 20,000,000 K are obtained from line ratios during flare rise phases in M as well as X flares, while in the decay phase the calcium temperature can be as low as 8,000,000 K, which is significantly lower than in X flares. Large nonthermal motions (on the order of 130 km/sec at most) are also observed in M as well as X flares, which are largest during the soft X-ray rise phase. Finally, it is shown that the method proposed by Gabriel and Phillips (1979) for detecting departures of electrons from Maxwellian velocity distributions is not sufficiently sensitive to give reliable results for the present data. Publication: The Astrophysical Journal Pub Date: November 1980 DOI: 10.1086/158434 Bibcode: 1980ApJ...241.1175F Keywords: Solar Flares; Solar Spectra; Solar X-Rays; X Ray Spectra; Electron Energy; High Resolution; Spectral Line Width; Solar Physics full text sources ADS | Related Materials (8) Part 1: 1979ApJ...233L.157D Part 2: 1980ApJ...238..365F Part 3: 1980ApJ...239..725D Part 5: 1981ApJ...245..315D Part 6: 1982ApJ...260..885F Part 7: 1985ApJ...292..309K Part 8: 1986ApJ...306..327K Part 9: 1989ApJ...345.1079D

Combining the Solar Dynamics Observatory and the New Vacuum Solar Telescope observations, we study a confined flare triggered by a rising flux rope within the trailing sunspots of active region 12733. The flux rope lying above the sheared polarity inversion line can be constructed through magnetic extrapolation but could not be detected in multiwavelength images at the pre-flare stage. The conspicuous shearing motions between the opposite-polarity fields in the photosphere are considered to be responsible for the flux rope formation. The maximum twist of the flux rope is as high as −1.76, and then the flux rope rises due to the kink instability. Only when the flare starts can the flux rope be observed in high-temperature wavelengths. The differential emission measure results confirm that this flux rope is a high-temperature structure. Associated with the rising flux rope, there appear many post-flare loops and a pair of flare ribbons. When the rising flux rope meets and reconnects with the large-scale overlying field lines, a set of large-scale twisted loops are formed, and two flare ribbons propagating in opposite directions appear on the outskirts of the former ribbons, indicating that the twist of the flux rope is transferred to a much larger system. These results imply that the external reconnection between the rising flux rope and the large-scale overlying loops plays an important role in the confined flare formation.

With observations of the Interface Region Imaging Spectrograph (IRIS), we study chromospheric heating and evaporation during an M1.6 flare SOL2015-03-12T11:50. At the flare ribbons, the Mg ii 2791.59 Å line shows quasi-periodic short-duration red-wing enhancement, which is likely related to repetitive chromospheric condensation as a result of episodic heating. On the contrary, the Si iv 1402.77 Å line reveals a persistent red-wing asymmetry in both the impulsive and decay phases, suggesting that this line responds to both cooling downflows and chromospheric condensation. The first two episodes of red-wing enhancement occurred around 11:42 UT and 11:45 UT, when two moving brightenings indicative of heating fronts crossed the IRIS slit. The greatly enhanced red wings of the Si iv and Mg ii lines at these occasions are accompanied by an obvious increase in the line intensities and the HXR flux, suggesting two episodes of energy injection into the lower atmosphere in the form of nonthermal electrons. The Mg ii k/h ratio has a small value of ∼1.2 at the ribbons and decreases to ∼1.1 at these two occasions. Correspondingly, the Fe xxi 1354 Å line reveals two episodes of chromospheric evaporation, which is characterized as a smooth decrease of the blueshift from ∼300 km s−1 to nearly zero within ∼3 minutes. The Fe xxi 1354 Å line is entirely blueshifted in the first episode, while it appears to contain a nearly stationary component and a blueshifted component in the second episode. Additional episodes of blueshifted Fe xxi emission are found around the northern ribbon in the decay phase, though no obvious response is detected in the Si iv and Mg ii emission. We have also examined the Fe xxi emission at the flare loop top and identified a secondary component with a ∼200 km s−1 redshift, which possibly results from the downward moving reconnection outflow. Our analysis also yields a rest wavelength of 1354.0878 ± 0.0072 Å for this Fe xxi line.

Using data from the Bragg crystal spectrometer on the Yohkoh spacecraft we have computed measures of the total intensity, centroid position, and line width for the resonance line of Ca xix during the rise phase and after maximum for 219 solar flares. The difference between the centroid positions early and late in each flare yields a measure of the line-of-sight velocity shift of the line centroid. We find a trend in the average value of the centroid shift with distance from Sun center suggesting radial mass motions with a characteristic velocity of 58 km s<SUP>-1</SUP>. There is a correlation between the rise-phase line widths and the centroid shift. We find no correlation between the centroid shift and the peak intensity, rise time, and total flare duration; and no correlation between the line width and the distance from Sun center, the peak intensity, rise time, and total flare duration. These results do not conclusively support or refute the simple electron-beam-driven model or the thermal model for the rise phase of a solar flare.

Wepresentthefirstquantitativecomparisonbetweenthetotalmagneticreconnectionfluxinthelowcoronainthe wake of coronal mass ejections (CMEs) and the magnetic flux in magnetic clouds (MCs) that reach 1 AU 2Y3 days after CME onset. The total reconnection flux is measured from flare ribbons, and the MC flux is computed using in situ observations at 1 AU, all ranging from 10 20 to 10 22 Mx. It is found that for the nine studied events in which the association between flares, CMEs,and MCs isidentified, the MCflux iscorrelatedwiththe total reconnection flux! r. Further, the poloidal (azimuthal) MC flux ! p is comparable with the reconnection flux ! r, and the toroidal (axial) MC flux ! t is a fraction of ! r. Events associated with filament eruption do not exhibit a different ! t, p-! r relation from events not accompanied by erupting filaments. The relations revealed between these independently measured physical quantities suggest that for the studied samples, the magnetic flux and twist of interplanetary magnetic flux ropes, reflected by MCs, are highly relevant to low-corona magnetic reconnection during the eruption. We discuss the implications of this result for the formation mechanism of twisted magnetic flux ropes, namely, whether the helical structure of themagnetic flux ropeis largelypre-existing or formed in situ by low-coronamagnetic reconnection.We alsomeasuremagneticfluxencompassedincoronaldimmingregions(! d)anddiscussitsrelationtothereconnection flux inferred from flare ribbons and MC flux.

Here we study a filament eruption on 2023 April 21. The filament was composed of two segments, named S1 and S2. Initially, the brightening and bidirectionally plasmoid flows appeared inside S1, and then the west part of S1 (WS1) experienced rapid rising and eruption, accompanied by coronal dimming, flare ribbons, and a secondary flare ribbon. However, the east part of S1 (ES1) rose slowly and was confined. The material within ES1 drained back to its eastern footpoint, resulting in the footpoint brightening. In the later phase, the south footpoint of the stable extreme-ultraviolet (EUV) loops overlying ES1 was brightened also, which may result from the disturbance of drainage. During S1 eruption and activation, S2 remained stable. Nonlinear force-free field extrapolation shows that the footpoints of the magnetic field lines overlying WS1 are rooted on the flare ribbons, while the field lines overlying ES1, which share a negative field with other lines, correspond to the stable EUV loops. Based on potential field extrapolation, we calculate the decay index of the background fields overlying the filament. It indicates that the critical height of the torus instability of the fields overlying WS1 is lower than that overlying ES1. To interpret this filament eruption, we first put forward the eruptive duality, characterized by the eruption of the partial filament structure and the confinement of the other structure, and this duality is determined by the properties of the overlying fields.

The solar flare is one of the most violent explosions, and can disturb the near-Earth space weather. Except for commonly single-peaked solar flares in soft X-ray, some special flares show intriguing a two-peak feature that is deserved much more attentions. Here, we reported a confined two-peaked solar flare and analyzed the associated eruptions using high-quality observations from Educational Adaptive-optics Solar Telescope and Solar Dynamics Observatory. Before the flare, a magnetic flux rope (MFR) formed through partially tether-cutting reconnection between two sheared arches. The flare occurred after the MFR eruption that was confined by the overlying strong field. Interestingly, a small underlying filament immediately erupted, which was possibly destabilized by the flare ribbon. The successive eruptions were confirmed by the analysis of the emission measure and the reconnection fluxes. Therefore, we suggest that the two peaks of the confined solar flare are corresponding to two episodes of magnetic reconnection during the successive eruptions of the MFR and the underlying filament.

Observationally, there is a small fraction of solar white-light flares (WLFs), the so-called type II WLFs, showing an increased visible continuum but no significant Balmer jump and less strong chromospheric line emission in comparison with type I WLFs. The classical point of view, that the flare energy is initially released in the corona and then transported downward, can hardly explain WLFs of this kind. In this paper we explore the possibility that type II WLFs originate from a deeper layer. Assuming an in situ energy release, in particular in the form of high-energy particles, in a region around the temperature minimum, the continuum emission is computed in different time stages during the flare evolution. At first, nonthermal excitation and ionization of hydrogen atoms caused by bombarding particles result in a decline of the visible continuum. Later on, the lower atmosphere is gradually heated through radiative transfer, mitigating the continuum decline. In the final stage, when the particle bombardment stops while the atmosphere still keeps a heated state, we obtain a positive continuum contrast without an obvious Balmer jump. This meets the condition required for type II WLFs. The presence or absence of a continuum decline in the early stage of the flare provides a diagnostic tool for nonthermal processes in the lower atmosphere.