Main Flare Research Articles

Searching for similarities in the accretion flow of Seyfert 1 galaxies and cataclysmic variables based on the flare profiles of IRAS 13224-3809, 1H 0707-495, Mrk 766, and MV Lyr

We studied the fast variability of three selected active galactic nuclei (AGNs), IRAS\,13224-3809, 1H\,0707-495, and Mrk\,766, and the cataclysmic variable MV\,Lyr, which were observed by the and spacecrafts, respectively. Our goal is to search for the common origin of the variability and to test the so-called sandwich model, in which a geometrically thick corona surrounds a geometrically thin disc. We studied the substructures of the averaged flare profiles. The flare profile method identifies individual flares in the light curve, and averages them. The direct fitting of the profile substructures identified individual characteristic frequencies that are seen in standard power density spectra (PDS) as a break frequency or quasi-periodic oscillation. The credibility of the flare profile substructures is demonstrated by comparison with the autocorrelation function. We found that the flare profiles of AGNs are similar to those of a cataclysmic variable in the low state. We explain this as a consequence of a truncated inner disc in a sandwich model. The same scenario is also able to explain the characteristic break frequencies in X-ray PDS, which are not seen in the optical. We also searched for substructures in the flare profile of IRAS\,13224-3809. In addition to a permanently present main flare, we found that a transient side-lobe appears before the main flare and is only seen in a high-flux period. The complex flare profile of this AGN suggests that an additional source of X-rays appears during the high-flux period. We propose a scenario in which an accretion flow fluctuation enters the sandwich corona and propagates further to some very central part of the accretion disc.

Stealth Non-standard-model Confined Flare Eruptions: Sudden Reconnection Events in Ostensibly Inert Magnetic Arches from Sunspots

We report seven examples of a long-ignored type of confined solar flare eruption that does not fit the standard model for confined flare eruptions. Because they are confined eruptions, do not fit the standard model, and unexpectedly erupt in ostensibly inert magnetic arches, we have named them stealth non-standard-model confined flare eruptions. Each of our flaring magnetic arches stems from a big sunspot. We tracked each eruption in full-cadence UV and EUV images from the Atmospheric Imaging Assembly of Solar Dynamics Observatory (SDO) in combination with magnetograms from SDO’s Helioseismic and Magnetic Imager. We present the onset and evolution of two eruptions in detail: one of six that each makes two side-by-side main flare loops, and one that makes two crossed main flare loops. For these two cases, we present cartoons of the proposed pre-eruption field configuration and how sudden reconnection makes the flare ribbons and flare loops. Each of the seven eruptions is consistent with being made by sudden reconnection at an interface between two internal field strands of the magnetic arch, where they cross at a small (10°–20°) angle. These stealth non-standard-model confined flare eruptions therefore plausibly support the idea of E. N. Parker for coronal heating in solar coronal magnetic loops by nanoflare bursts of reconnection at interfaces of internal field strands that cross at angles of 10°–20°.

High-energy insights from an escaping coronal mass ejection with Solar Orbiter/STIX observations

Solar eruptive events, including solar flares and coronal mass ejections (CMEs), are typically characterised by energetically significant X-ray emissions from flare-accelerated electrons and hot thermal plasmas. However, the intense brightness of solar flares often overshadows high-coronal X-ray emissions from the associated eruptions due to the limited dynamic range of current instrumentation. Occulted events, where the main flare is blocked by the solar limb, provide an opportunity to observe and analyse the X-ray emissions specifically associated with CMEs. This study investigates the X-ray and extreme ultraviolet (EUV) emissions associated with a large filament eruption and CME that occurred on February 15, 2022. This event was highly occulted from the three vantage points of Solar Orbiter (sim 45$^ circ $ behind the limb), Solar–TErrestrial RElations Observatory (STEREO-A), and Earth. We utilised X-ray observations from the Spectrometer/Telescope for Imaging X-rays (STIX) and EUV observations from the Full Sun Imager (FSI) of the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter, supplemented by multi-viewpoint observations from STEREO-A/Extreme-UltraViolet Imager (EUVI). This enabled a comprehensive analysis of the X-ray emissions in relation to the filament structure observed in the EUV. We used STIX's imaging and spectroscopy capabilities to characterise the X-ray source associated with the eruption. Our analysis reveals that the X-ray emissions associated with the occulted eruption originate from an altitude exceeding 0.3 \(R_ above the main flare site. The X-ray time profile shows a sharp increase and exponential decay, and consists of both a hot thermal component at 17pm 2 MK and non-thermal emissions ($>11.4 keV) characterised by an electron spectral index of 3.9pm 0.2. Imaging analysis shows an extended X-ray source that coincides with the EUV emission as observed from EUI, and was imaged until the source grew to a size exceeding the STIX imaging limit (180 arcsec). Filament eruptions and associated CMEs have hot and non-thermal components, and the associated X-ray emissions are energetically significant. Our findings demonstrate that STIX combined with EUI provides a unique and powerful tool for examining the energetic properties of the CME component of solar energetic eruptions. Multi-viewpoint and multi-instrument observations are crucial for revealing such energetically significant sources in solar eruptions that might otherwise remain obscured.

Evidence for flare-accelerated particles in large scale loops in the behind-the-limb gamma-ray solar flare of September 29, 2022

We report on the detection of the gamma-ray emission above 100 MeV from the solar flare of September 29, 2022, by Fermi LAT with simultaneous coverage in HXR by Solar Orbiter STIX. The Solar Orbiter-Earth separation was 178° at the time of the flare as seen from Earth, with Solar Orbiter observing the east limb. Based on STIX imaging, the flare was located 16° behind the eastern limb as seen from Earth. The STIX and GBM non-thermal emission and the LAT emission above 100 MeV all show similarly shaped time profiles, and the Fermi profiles peaked only 20 s after the STIX signal from the main flare site, setting this flare apart from all the other occulted flares observed by Fermi LAT. The radio spectral imaging based on the Nançay Radioheliograph and ORFEES spectrograph reveal geometries consistent with a magnetic structure that connects the parent active region behind the limb to the visible disk. We studied the basic characteristics of the gamma-ray time profile, in particular, the rise and decay times and the time delay between the gamma-ray and HXR peak fluxes. We compared the characteristics of this event with those of four Fermi LAT behind-the-limb flares and with an on-disk event and found that this event is strikingly similar to the impulsive on-disk flare. Based on multiwavelength observations, we find that the gamma-ray emission above 100 MeV originated from ions accelerated in the parent active region behind the limb and was transported to the visible disk via a large magnetic structure connected to the parent active region behind the limb. Our results strongly suggest that the source of the emission above 100 MeV from the September 29, 2022 flare cannot be the CME-driven shock.

Spectral Features of the Solar Transition Region and Chromospheric Lines at Flare Ribbons Observed with IRIS

We report on the spectral features of the Si iv λ1402.77, C ii λ1334.53, and Mg ii h or k lines, formed in the layers from the transition region to the chromosphere, in three two-ribbon flares (with X, M, and C class) observed with IRIS. All three lines show significant redshifts within the main flare ribbons, which mainly originate from the chromospheric condensation during the flares. The average redshift velocities of the Si iv line within the main ribbons are 56.6, 25.6, and 10.5 km s−1 for the X-, M-, and C-class flares, respectively, which show a decreasing tendency with the flare class. The C ii and Mg ii lines show a similar tendency but with smaller velocities compared to the Si iv line. Additionally, the Mg ii h or k line shows a blue-wing enhancement in the three flares, in particular at the flare ribbon fronts, which is supposed to be caused by an upflow in the upper chromosphere due to the heating of the atmosphere. Moreover, the Mg ii h or k line exhibits a central reversal at the flare ribbons but turns to pure emission shortly after 1–4 minutes. Correspondingly, the C ii line also shows a central reversal but in a smaller region. However, for the Si iv line, the central reversal is only found in the X-class flare. As usual, the central reversal of these lines can be caused by the opacity effect. This implies that, in addition to the optically thick lines (C ii and Mg ii lines), the Si iv line can become optically thick in a strong flare, which is likely related to the nonthermal electron beam heating.

Preflare X-Ray Pulsations with Sources Outside the Main Flare Active Region

Earlier, we showed that according to the nature of the location of sources of preflare X-ray pulsationsrelative to the main solar flare, events are divided into at least two types: in type I events, the sources ofpulsations and the main flare are in the same active region (AR) and in type II events they are in differentregions. This paper presents an analysis of a type II event in which, according to data from the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) space observatory, X-ray sources of preflare quasi-periodicpulsations (with a period P = 1.5 ± 0.1 min), which began at ~1802 UT, were located in AR 11884 in the WesternHemisphere, and the sources of the main flare M1.0 SOL2013-11-05T18:08 were located in AR 11890 inthe Eastern Hemisphere. The pulsations were also observed with the Gamma-Ray Burst Monitor (GBM)aboard the Fermi space observatory and the X-Ray Sensor (XRS) aboard the Geostationary OperationalEnvironmental Satellite (GOES), excluding the possibility of their artificial origin. According to the data ofthe Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO) in the extremeultraviolet range, it was found that the sources of pulsations were located at the base of coronal jets that flowedout at velocities of ~100–1500 km/s. The distance between AR 11884 and AR 11890 was ~1.4 RS. It wouldtake ~17–250 min for the jet plasma to reach AR 11890, which is much longer than the time interval betweenthe onset of pulsations (jets) and the flare (~6 min). No loops connecting AR 11884 and AR 11890 wereobserved in the corona. Moreover, no connection of these regions by magnetic field lines extrapolated fromthe photosphere to the corona in the potential approximation was found. These arguments indicate that thejets (and associated pulsations) could not be the trigger for the flare. Thus, a vivid example of an event is presentedin which there was no physical connection between preflare X-ray pulsations (and jets) and the flarethat followed them. This event demonstrates the importance of spatially resolved observations in the study ofpulsations on the Sun and stars.

Preflare X-ray Pulsations with Sources Outside the Main Flare Active Region

Preflare X-ray Pulsations with Sources Outside the Main Flare Active Region

Sequential Remote Brightenings and Co-spatial Fast Downflows during Two Successive Flares

Remote brightenings often appear at the outskirts of the active regions of solar eruptive events. Nevertheless, their origin remains to be ascertained. In this study, we report imaging and spectroscopic observations of sequential remote brightenings with a combination of observations from the Hα Imaging Spectrograph on board the Chinese Hα Solar Explorer, which is the first space-based solar telescope of China, and from the Solar Dynamics Observatory. It is found that during two successive M-class flares occurring on 2022 August 17 multiple ribbon-like brightenings appeared in sequence away from the flaring active region. Meanwhile, abundant cool filament materials moved downward to the sequential remote brightenings, which were visible at the Hα red wing with a line-of-sight speed of up to 70 km s−1. The extrapolated three-dimensional magnetic field configuration shows that the sequential remote brightenings correspond to the footpoints of closed ambient field lines whose conjugate footpoints are rooted in the main flare site. We suggest that the sequential remote brightenings are most likely to be caused by the heating of the interchange reconnection between the erupting flux rope and the closed ambient field, during which the rope-hosting filament materials are transferred to the periphery of the flaring active region along the closed ambient field rather than to the interplanetary space, such as in the scenario of slow solar wind formation.

Synchrotron Radiation Dominates the Extremely Bright GRB 221009A

The brightest gamma-ray burst, GRB 221009A, has spurred numerous theoretical investigations, with particular attention paid to the origins of ultrahigh-energy TeV photons during the prompt phase. However, analyzing the mechanism of radiation of photons in the ∼MeV range has been difficult because the high flux causes pileup and saturation effects in most GRB detectors. In this Letter, we present systematic modeling of the time-resolved spectra of the GRB using unsaturated data obtained from the Fermi Gamma-ray Burst Monitor (precursor) and SATech-01/GECAM-C (main emission and flare). Our approach incorporates the synchrotron radiation model, which assumes an expanding emission region with relativistic speed and a global magnetic field that decays with radius, and successfully fits such a model to the observational data. Our results indicate that the spectra of the burst are fully in accordance with a synchrotron origin from relativistic electrons accelerated at a large emission radius. The lack of thermal emission in the prompt emission spectra supports a Poynting flux–dominated jet composition.

Solar flare hard X-rays from the anchor points of an eruptive filament

Context.We present an analysis of a GOES M1.8 flare with excellent observational coverage in UV, extreme-UV (EUV), and X-ray, including observations from the Interface Region Imaging Spectrograph (IRIS), from the Solar Dynamics Observatory (SDO) with the Atmospheric Imaging Assembly (AIA), from the Hinode/EUV Imaging Spectrometer (EIS), from the Hinode/X-ray Telescope (XRT), and from Solar Orbiter with the Spectrometer/Telescope for Imaging X-rays (STIX). Hard X-ray emission is often observed at the footpoints of flare loops and is occasionally observed in the corona. In this flare, four nonthermal hard X-ray sources are seen.Aims.Our aim is to understand why we can observe four individual nonthermal sources in this flare and how we can characterize the physical properties of these four sources.Methods.We used the multiwavelength approach to analyze the flare and characterize the four sources. To do this, we combined imaging at different wavelengths and spectroscopic fitting in the EUV and X-ray range.Results.The flare is eruptive with an associated coronal mass ejection, and it shows the classical flare picture of a heated flare loop seen in EUV and X-rays, and two nonthermal hard X-ray footpoints at the loop ends. In addition to the main flare sources, we observed two outer sources in the UV, EUV, and nonthermal X-ray range located away from the main flare loop to the east and west. The two outer sources are clearly correlated in time, and they are only seen during the first two minutes of the impulsive phase, which lasts a total of about four minutes.Conclusions.Based on the analysis, we determine that the outer sources are the anchor points of an erupting filament. The hard X-ray emission is interpreted as flare-accelerated electrons that are injected upward into the filament and then precipitate along the filament toward the chromosphere, producing Bremsstrahlung. While sources like this have been speculated to exist, this is the first report of their detection.

Formation and Eruption of Hot Channels during an M6.5 Class Solar Flare

We investigate the formation and eruption of hot channels associated with the M6.5 class flare (SOL 2015-06-22T18:23) that occurred in NOAA AR 12371 on 2015 June 22. Two flare precursors are observed before the flare’s main phase. Observations in 94 and 131 Å by SDO/AIA revealed the early morphology of the first hot channel as a group of hot loops, termed the seed hot channel. A few seed hot channels are formed above the polarity inversion line (PIL) and the formation is associated with the parallel motion of the footpoint brightenings along the PIL, which proceeds into the early stage of the flare main phase. During this process, seed hot channels build up and rise slowly, accelerating at the peak of the second precursor. They merge during the process of acceleration, forming a larger hot channel, which then forms an inverted-γ-shape kinking structure. Before the flare peak, the second kinking hot channel with negative crossing appears near the first kinking hot channel that erupted. The eruption of these two hot channels produces two peaks on the main flare's GOES light curve. The propagation of the footpoint brightenings along the PIL indicates that the first kinking hot channel may be formed due to zipper reconnection. The occurrence of merging between seed hot channels observed by AIA is supported by the extrapolated nonlinear force-free field models. The observed writhing motion of the first kinking hot channel may be driven by the Lorentz force.

An outline of Paleoproterozoic-Mesoproterozoic crustal evolution of the NW Amazon craton and implications for the Columbia Supercontinent

ABSTRACT The Rio Negro Province in the NW Amazon craton is composed of three domains (northeastern, central, and southwestern) in turn separated into several regional terrains, showing main NE-SW and WNW-ESE structures and being composed of high-grade polydeformed basement with 1840–1700 Ma protolith ages. The Northeastern Domain shows basements dominated by high-K calc-alkaline to shoshonitic metagranitoids, orthogneisses, migmatites, augen gneisses, and local A-type leucogneisses (1810–1760 Ma, Cauaburi Complex). In Venezuela, this basement is not widely known, but encompasses the oldest rocks of the province (1840–1820 Ma, San Carlos Metamorphic Terrane). The Southwestern Domain comprises medium- to high-K calc-alkaline orthogneisses (Querari Complex) with an extended compositional range (diorite to granite), NE-trending main foliation, and 1740–1700 Ma protolith ages. The Central Domain comprises peraluminous crustal-derived granites (1520–1480 Ma), supracrustal rocks, paragneisses, and some Cauaburi Complex inliers. The Nd isotope data for the basement rocks indicates mantle sources with decreasing crustal contributions and younger TDM ages from east (2.54–1.96 Ga) to west (1.97–1.82 Ga). The Rio Negro Province is interpreted as an accretionary orogen formed by a long-lived magmatic arc system active during three phases: 1.84–1.82 Ga, 1.81–1.76 Ga (main flare up) and 1.75–1.70 Ga. Later, this arc system was affected by collisional orogenies at ~1500 Ma (Içana Orogeny) and ~1300 Ma (Putumayo Orogeny), as showed by the Ar–Ar step heating plateau ages (biotite, hornblende) and U-Pb SHRIMP ages (zircon, titanite) recording two main metamorphic events at 1520–1480 Ma (medium–high T) and 1400–1310 Ma (low–medium T), with important tectonothermal effects also further east in the Tapajós-Parima Province. Based on similar accretionary histories, the Rio Negro Province has also apparent long-lived connections with Laurentia and Baltica (Transscandinavian Belt), forming the core of the Columbia Supercontinent.

The X-Ray Outburst of PG 1553+113: A Precession Effect of Two Jets in the Supermassive Black Hole Binary System

Abstract Blazar PG 1553+113 is thought to be a host of supermassive black hole binary system. A 2.2 yr quasi-periodicity in the γ-ray light curve was detected, possibly a result of jet precession. Motivated by the previous studies based on the γ-ray data, we analyzed the X-ray light curve and spectra observed during 2012–2020. The 2.2 yr quasi-periodicity might be consistent with the main-flare recurrence in the X-ray light curve. When a weak rebrightening in the γ-ray was observed, a corresponding relatively strong brightening in the X-ray light curve can be identified. The harder-when-brighter tendency in both X-ray main and weak flares was shown, as well as a weak softer-when-brighter behavior for the quiescent state. We explore the possibility that the variability in the X-ray band can be interpreted with two-jet precession scenario. Using the relation between jets and accretion disks, we derive the primary black hole mass ≃3.47 × 108 M ☉ and mass of the secondary one ≃1.40 × 108 M ☉, and their mass ratio ∼0.41.

Multiple Electron Acceleration Instances during a Series of Solar Microflares Observed Simultaneously at X-Rays and Microwaves

Abstract Even small solar flares can display a surprising level of complexity regarding their morphology and temporal evolution. Many of their properties, such as energy release and electron acceleration can be studied using highly complementary observations at X-ray and radio wavelengths. We present X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager and radio observations from the Karl G. Jansky Very Large Array (VLA) of a series of GOES A3.4–B1.6 class flares observed on 2013 April 23. The flares, as seen in X-ray and extreme ultraviolet, originated from multiple locations within active region NOAA 11726. A veritable zoo of different radio emissions between 1 GHz and 2 GHz was observed cotemporally with the X-ray flares. In addition to broadband continuum emission, broadband short-lived bursts and narrowband spikes, indicative of accelerated electrons, were observed. However, these sources were located up to 150″ away from the flaring X-ray sources but only some of these emissions could be explained as signatures of electrons that were accelerated near the main flare site. For other sources, no obvious magnetic connection to the main flare site could be found. These emissions likely originate from secondary acceleration sites triggered by the flare, but may be due to reconnection and acceleration completely unrelated to the cotemporally observed flare. Thanks to the extremely high sensitivity of the VLA, not achieved with current X-ray instrumentation, it is shown that particle acceleration happens frequently and at multiple locations within a flaring active region.

Extreme-ultraviolet Late Phase in Homologous Solar Flares from a Complex Active Region

Abstract Recent observations in extreme-ultraviolet (EUV) wavelengths reveal a new late phase in some solar flares, which is seen as a second peak in warm coronal emissions (∼3 MK) several tens of minutes to a few hours after the soft X-ray peak. The origin of the EUV late phase (ELP) is explained by either a long-lasting cooling process in the long ELP loops or a delayed energy ejection into the ELP loops well after the main flare heating. Using the observations with the Solar Dynamics Observatory, we investigate the production of the ELP in six homologous flares (F1–F6) originating from a complex active region (AR), NOAA Active Region 11283, with an emphasis on the emission characteristics of the flares. It is found that the main production mechanism of the ELP changes from additional heating in flare F1 to long-lasting cooling in flares F3–F6, with both mechanisms playing a role in flare F2. The transition is evidenced by an abrupt decrease of the time lag of the ELP peak, and the long-lasting cooling process in the majority of the flares is validated by a positive correlation between the flare ribbon fluence and the ELP peak intensity. We attribute the change in ELP production mechanism to an enhancement of the envelope magnetic field above the AR, which facilitates a more prompt and energetic heating of the ELP loops. In addition, the last and the only confined flare F6 exhibits an extremely large ELP. The different emission pattern revealed in this flare may reflect a different energy partitioning inside the ELP loops, which is due to a different magnetic reconnection process.

The impact and recovery of asteroid 2018 LA.

The June 2, 2018, impact of asteroid 2018 LA over Botswana is only the second asteroid detected in space prior to impacting over land. Here, we report on the successful recovery of meteorites. Additional astrometric data refine the approach orbit and define the spin period and shape of the asteroid. Video observations of the fireball constrain the asteroid's position in its orbit and were used to triangulate the location of the fireball's main flare over the Central Kalahari Game Reserve. 23 meteorites were recovered. A consortium study of eight of these classifies Motopi Pan as a HED polymict breccia derived from howardite, cumulate and basaltic eucrite, and diogenite lithologies. Before impact, 2018 LA was a solid rock of ~156 cm diameter with high bulk density ~2.85 g/cm3, a relatively low albedo pv ~ 0.25, no significant opposition effect on the asteroid brightness, and an impact kinetic energy of ~0.2 kt. The orbit of 2018 LA is consistent with an origin at Vesta (or its Vestoids) and delivery into an Earth-impacting orbit via the v6 resonance. The impact that ejected 2018 LA in an orbit towards Earth occurred 22.8 ± 3.8 Ma ago. Zircons record a concordant U-Pb age of 4563 ± 11 Ma and a consistent 207Pb/206Pb age of 4563 ± 6 Ma. A much younger Pb-Pb phosphate resetting age of 4234 ± 41 Ma was found. From this impact chronology, we discuss what is the possible source crater of Motopi Pan and the age of Vesta's Veneneia impact basin.

Evaluation of Different Flare Gas Recovery Alternatives with Exergy and Exergoeconomic Analyses

Natural gas flaring is considered one of the significant sources of greenhouse gas emissions in the upstream oil and gas industry. It plays an essential role in reducing the energy efficiency of oil and gas production. Depending on flare gas properties, it can be used for different destinations. Herein, we have evaluated the main flare gas recovery alternatives, including sweet gas production, Gas to Liquid (GTL), and power generation, by using exergy and exergoeconomic analysis tools. For this purpose, flare gas condition in two phases of the Pars Special Economic Energy Zone in south of Iran was chosen as a case study. The mass sensitivity analysis is conducted to examine the processes in different flare gas volumes. Mass flow fluctuation analysis is carried out to analyze the effect of mass flow fluctuation as an intrinsic characteristic of flare systems. Results indicate that the production of electrical power from flaring gas is an economical method regarding the exergoeconomic criteria. While the power generation process has disadvantages such as high exergy destruction and high capital cost, advantages such as higher revenue, local potentials for designing, equipment, and construction should be regarded. On the other hand, the sweetening plant has the highest exergetic efficiency rather than other substitutes. This method also has a lower exergoeconomic factor, especially in lower flaring volume. The mass flow sensitivity analysis in these processes shows the GTL production unit's appropriate performance in low flare gas volume. The results also offer the superior performance of sweetening plants in high flare gas volume. Combined Cycle Power Plant (CCPP) process shows an acceptable performance in a broad range of flare gas volumes. Additionally, mass flow fluctuation analysis has been conducted to determine the effect of mass flow fluctuation in these alternatives. The investigation suggested that the CCPP process has lower fluctuation in terms of cycle product (power generation).

Neoproterozoic magmatic arc volcanism in the Borborema Province, NE Brazil: possible flare-ups and lulls and implications for western Gondwana assembly

New zircon U-Pb (SHRIMP and LA-ICPMS), elemental and Nd-Sr geochemistry data on rhyolitic metavolcanic and metavolcaniclastic rocks of NE Brazil characterize widespread arc-related phenomena during the Neoproterozoic, related to the Conceição-type or Stage I plutonic rocks. U-Pb zircon dating pinpoint the main phase of magmatic activity at ca. 635-600 Ma in the 700-km long sigmoidal Piancó-Alto Brígida domain, but other important flare-ups might have taken place at ca. 670-690, 730-760, 810-820 and 860-880 Ma. A comprehensive compilation of detrital zircon data from metavolcanosedimentary successions of the entire Borborema Province (n=5532) confirms the occurrence of a quasi-continuum Neoproterozoic spectra punctuated by peaks at those same age intervals separated by minor lulls. Low Th/U rims of zircon crystals dated at ca. 577 Ma provide an estimate of the age of regional transpressional metamorphism. Samples of all age ranges are mostly calc-alkaline, magnesian and peraluminous, with moderately to highly fractionated LREE enrichment, negative Nb-Ta anomalies akin to convergent settings, and plot mainly within the volcanic arc field in tectonic discrimination diagrams. Nd-Sr isotope systematics indicate the involvement of juvenile Neoproterozoic melts from the mantle wedge, which upon mixing with Archean-Paleoproterozoic basement and contamination with the host metasedimentary rocks yield Mesoproterozoic TDM mainly at 1.14-1.44 Ga, near-chondritic εNd(t) and 87Sr/86Sri 0.703-0.710. We put forward a model involving a major continental back-arc zone related to the development of the Conceição magmatic arc, akin to the modern-day Taupo volcanic zone of New Zealand, crosscutting NE Brazil and presumably continuing through the schist belts of Nigeria and Cameroon. The main magmatic flare ups might have been induced by extra-arc phenomena, such as collision of the West African paleocontinent with the northwestern Borborema edge due to closure of the exterior Goiás-Pharusian Ocean, force-speeding subduction in the interior V-shaped oceanic basins that constituted the Transnordestino-Central African Ocean and generating clockwise windshield-wiper-like rotation of the blocks back towards the São Francisco-Congo paleocontinent in a complete Wilson Cycle.

High-resolution He I 10830 Å Narrowband Imaging for an M-class Flare. III. EUV Late Phase

Abstract In this paper, we report the EUV late phase for the M1.8 class flare on 2012 July 5 in the active region (AR) 11515. The late phase is shown by the prominent appearance of EUV emission at 131 Å of two additional flare loop systems (flare arcades 2 and 3, as named in this paper) other than the main flare loop (flare arcade 1), as observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO). Three sets of flare arcades connect four flare ribbons, which forms an asymmetric quadrupole magnetic field configuration. While the emission from flare arcade 2, linking the pair of secondary flare ribbons, and arcade 3, linking one of the main flare ribbons and one of the secondary flare ribbons, conjointly contributes to the EUV late phase, their heating mechanisms are quite different. While the brightening of flare arcade 2 is the result of disturbance created by the eruption of EUV hot channels to the overlying coronal magnetic field, the heating of flare arcade 3 was closely associated with two rapid contractions of the overlying filament threads during the partial eruption of the filament. The contractions are discernible in He i 10830 Å images and have signatures in the EUV wavelengths of AIA. The two rapid contractions are the result of a sudden drop in magnetic pressure after the eruption of two hot channels. Clear evidence suggests that magnetic reconnection may occur between the contracting filament threads and the low-lying magnetic field.

Hot Plasma Flows and Oscillations in the Loop-top Region During the 2017 September 10 X8.2 Solar Flare

Abstract In this study, we investigate motions in the hot plasma above the flare loops during the 2017 September 10 X8.2 flare event. We examine the region to the south of the main flare arcade, where there is data from the Interface Region Imaging Spectrograph (IRIS) and the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. We find that there are initial blueshifts of 20–60 km s−1 observed in this region in the Fe xxi line in IRIS and the Fe xxiv line in EIS, and that the locations of these blueshifts move southward along the arcade over the course of about 10 minutes. The cadence of IRIS allows us to follow the evolution of these flows, and we find that at each location where there is an initial blueshift in the Fe xxi line, there are damped oscillations in the Doppler velocity with periods of ∼400 s. We conclude that these periods are independent of loop length, ruling out magnetoacoustic standing modes as a possible mechanism. Microwave observations from the Expanded Owens Valley Solar Array (EOVSA) indicate that there are nonthermal emissions in the region where the Doppler shifts are observed, indicating that accelerated particles are present. We suggest that the flows and oscillations are due to motions of the magnetic field that are caused by reconnection outflows disturbing the loop-top region.