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Energetic Electron Distribution of the Coronal Acceleration Region: First Results from Joint Microwave and Hard X-Ray Imaging SpectroscopyChen, BinBattaglia, MarinaKrucker, SämReeves, Katharine K.Glesener, LindsayDOI: info:10.3847/2041-8213/abe471v. 908L55
Chen, Bin, Battaglia, Marina, Krucker, Säm, Reeves, Katharine K., and Glesener, Lindsay. 2021. "Energetic Electron Distribution of the Coronal Acceleration Region: First Results from Joint Microwave and Hard X-Ray Imaging Spectroscopy." The Astrophysical Journal 908:L55.
ID: 159627
Type: article
Authors: Chen, Bin; Battaglia, Marina; Krucker, Säm; Reeves, Katharine K.; Glesener, Lindsay
Abstract: Nonthermal sources located above bright flare arcades, referred to as the "above-the-loop-top" sources, have been often suggested as the primary electron acceleration site in major solar flares. The X8.2 limb flare on 2017 September 10 features such an above-the-loop-top source, which was observed in both microwaves and hard X-rays (HXRs) by the Expanded Owens Valley Solar Array and the Reuven Ramaty High Energy Solar Spectroscopic Imager, respectively. By combining the microwave and HXR imaging spectroscopy observations with multifilter extreme ultraviolet and soft X-ray imaging data, we derive the coronal magnetic field and energetic electron distribution of the source over a broad energy range from 6.0. Temporally resolved analysis suggests that the electron distribution above the break energy rapidly hardens with the spectral index decreasing from >20 to ∼6.0 within 20 s, or less than ∼10 Alfvén crossing times in the source. These results provide strong support for the above-the-loop-top source as the primary site where an ongoing bulk acceleration of energetic electrons is taking place very early in the flare energy release.
Imaging Spectroscopy of CME-associated Solar Radio Bursts using OVRO-LWAChhabra, SherryGary, Dale E.Hallinan, GreggAnderson, Marin M.Chen, BinGreenhill, Lincoln J.Price, Danny C.DOI: info:10.3847/1538-4357/abc94bv. 906132
Chhabra, Sherry, Gary, Dale E., Hallinan, Gregg, Anderson, Marin M., Chen, Bin, Greenhill, Lincoln J., and Price, Danny C. 2021. "Imaging Spectroscopy of CME-associated Solar Radio Bursts using OVRO-LWA." The Astrophysical Journal 906:132.
ID: 159352
Type: article
Authors: Chhabra, Sherry; Gary, Dale E.; Hallinan, Gregg; Anderson, Marin M.; Chen, Bin; Greenhill, Lincoln J.; Price, Danny C.
Abstract: We present the first results of a solar radio event observed with the Owens Valley Radio Observatory Long Wavelength Array at metric wavelengths. We examine a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection (CME) and an M2.1 GOES soft X-ray flare from 2015 September 20. Images of 9 s cadence are used to analyze the event over a 120 minute period, and solar emission is observed out to a distance of ≍3.5 R, with an instantaneous bandwidth covering 22 MHz within the frequency range of 40-70 MHz. We present our results from the investigation of the radio event, focusing particularly on one burst source that exhibits outward motion, which we classify as a moving type IV burst. We image the event at multiple frequencies and use the source centroids to obtain the velocity for the outward motion. Spatial and temporal comparison with observations of the CME in white light from the C2 coronagraph of the Large Angle and Spectrometric COronagraph, indicates an association of the outward motion with the core of the CME. By performing graduated-cylindrical-shell reconstruction of the CME, we constrain the density in the volume. The electron plasma frequency obtained from the density estimates do not allow us to completely dismiss plasma emission as the underlying mechanism. However, based on source height and smoothness of the emission in frequency and time, we argue that gyrosynchrotron is the more plausible mechanism. We use gyrosynchrotron spectral-fitting techniques to estimate the evolving physical conditions during the outward motion of this burst source.
Measurement of magnetic field and relativistic electrons along a solar flare current sheetChen, BinShen, ChengcaiGary, Dale E.Reeves, Katharine K.Fleishman, Gregory D.Yu, SijieGuo, FanKrucker, SämLin, JunNita, Gelu M.Kong, XiangliangDOI: info:10.1038/s41550-020-1147-7v. 41140–1147
Chen, Bin, Shen, Chengcai, Gary, Dale E., Reeves, Katharine K., Fleishman, Gregory D., Yu, Sijie, Guo, Fan, Krucker, Säm, Lin, Jun, Nita, Gelu M., and Kong, Xiangliang. 2020. "Measurement of magnetic field and relativistic electrons along a solar flare current sheet." Nature Astronomy 4:1140– 1147.
ID: 158872
Type: article
Authors: Chen, Bin; Shen, Chengcai; Gary, Dale E.; Reeves, Katharine K.; Fleishman, Gregory D.; Yu, Sijie; Guo, Fan; Krucker, Säm; Lin, Jun; Nita, Gelu M.; Kong, Xiangliang
Abstract: In the standard model of solar flares, a large-scale reconnection current sheet is postulated to be the central engine for powering the flare energy release1-3 and accelerating particles4-6. However, where and how the energy release and particle acceleration occur remain unclear owing to the lack of measurements of the magnetic properties of the current sheet. Here we report the measurement of the spatially resolved magnetic field and flare-accelerated relativistic electrons along a current-sheet feature in a solar flare. The measured magnetic field profile shows a local maximum where the reconnecting field lines of opposite polarities closely approach each other, known as the reconnection X point. The measurements also reveal a local minimum near the bottom of the current sheet above the flare loop-top, referred to as a `magnetic bottle'. This spatial structure agrees with theoretical predictions1,7 and numerical modelling results. A strong reconnection electric field of about 4,000 V m-1 is inferred near the X point. This location, however, shows a local depletion of microwave-emitting relativistic electrons. These electrons instead concentrate at or near the magnetic bottle structure, where more than 99% of them reside at each instant. Our observations suggest that the loop-top magnetic bottle is probably the primary site for accelerating and confining the relativistic electrons.
Microwave Spectral Imaging of an Erupting Magnetic Flux Rope: Implications for the Standard Solar Flare Model in Three DimensionsChen, BinYu, SijieReeves, Katharine K.Gary, Dale E.DOI: info:10.3847/2041-8213/ab901av. 895L50
Chen, Bin, Yu, Sijie, Reeves, Katharine K., and Gary, Dale E. 2020. "Microwave Spectral Imaging of an Erupting Magnetic Flux Rope: Implications for the Standard Solar Flare Model in Three Dimensions." The Astrophysical Journal 895:L50.
ID: 156815
Type: article
Authors: Chen, Bin; Yu, Sijie; Reeves, Katharine K.; Gary, Dale E.
Abstract: We report microwave spectral imaging observations of an erupting magnetic flux rope during the early impulsive phase of the X8.2-class limb flare on 2017 September 10, obtained by the Expanded Owens Valley Solar Array. A few days prior to the eruption, when viewed against the disk, the flux rope appeared as a reverse S-shaped dark filament along the magnetic polarity inversion line. During the eruption, the rope exhibited a "hot channel" structure in extreme ultraviolet and soft X-ray passbands sensitive to ∼10 MK plasma. The central portion of the flux rope was nearly aligned with the line of sight, which quickly developed into a teardrop-shaped dark cavity during the early phase of the eruption. A long and thin plasma sheet formed below the cavity, interpreted as the reconnection current sheet viewed edge on. A nonthermal microwave source was present at the location of the central current sheet, which extended upward encompassing the dark cavity. A pair of nonthermal microwave sources were observed for several minutes on both sides of the main flaring region. They shared a similar temporal behavior and spectral property to the central microwave source below the cavity, interpreted as the conjugate footpoints of the erupting flux rope. These observations are broadly consistent with the magnetic topology and the associated energy release scenario suggested in the three-dimensional standard model for eruptive solar flares. In particular, our detection of nonthermal emission at conjugate flux rope footpoints provides solid evidence of particle transport along an erupting magnetic flux rope.
Dynamical Modulation of Solar Flare Electron Acceleration due to Plasmoid-shock Interactions in the Looptop RegionKong, XiangliangGuo, FanShen, ChengcaiChen, BinChen, YaoGiacalone, JoeDOI: info:10.3847/2041-8213/abcbf5v. 905L16
Kong, Xiangliang, Guo, Fan, Shen, Chengcai, Chen, Bin, Chen, Yao, and Giacalone, Joe. 2020. "Dynamical Modulation of Solar Flare Electron Acceleration due to Plasmoid-shock Interactions in the Looptop Region." The Astrophysical Journal 905:L16.
ID: 158762
Type: article
Authors: Kong, Xiangliang; Guo, Fan; Shen, Chengcai; Chen, Bin; Chen, Yao; Giacalone, Joe
Abstract: A fast-mode shock can form in the front of reconnection outflows and has been suggested as a promising site for particle acceleration in solar flares. Recent developments in the study of magnetic reconnection have shown that numerous plasmoids can be produced in a large-scale current layer. Here we investigate the dynamical modulation of electron acceleration in the looptop region when plasmoids intermittently arrive at the shock by combining magnetohydrodynamics simulations with a particle kinetic model. As plasmoids interact with the shock, the looptop region exhibits various compressible structures that modulate the production of energetic electrons. The energetic electron population varies rapidly in both time and space. The number of 5-10 keV electrons correlates well with the compression area, while that of >50 keV electrons shows good correlation with the strong compression area but only moderate correlation with shock parameters. We further examine the impacts of the first plasmoid, which marks the transition from a quasi-steady shock front to a distorted and dynamical shock. The number of energetic electrons is reduced by ˜20% at 15-25 keV and nearly 40% for 25-50 keV, while the number of 5-10 keV electrons increases. In addition, the electron energy spectrum above 10 keV evolves softer with time. We also find that double or even multiple distinct sources can develop in the looptop region when the plasmoids move across the shock. Our simulations have strong implications to the interpretation of nonthermal looptop sources, as well as the commonly observed fast temporal variations in flare emissions, including the quasi-periodic pulsations.
Hot Plasma Flows and Oscillations in the Loop-top Region During the 2017 September 10 X8.2 Solar FlareReeves, Katharine K.Polito, VanessaChen, BinGalan, GiselleYu, SijieLiu, WeiLi, GangDOI: info:10.3847/1538-4357/abc4e0v. 905165
Reeves, Katharine K., Polito, Vanessa, Chen, Bin, Galan, Giselle, Yu, Sijie, Liu, Wei, and Li, Gang. 2020. "Hot Plasma Flows and Oscillations in the Loop-top Region During the 2017 September 10 X8.2 Solar Flare." The Astrophysical Journal 905:165.
ID: 158794
Type: article
Authors: Reeves, Katharine K.; Polito, Vanessa; Chen, Bin; Galan, Giselle; Yu, Sijie; Liu, Wei; Li, Gang
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.
Magnetic Reconnection during the Post-impulsive Phase of a Long-duration Solar Flare: Bidirectional Outflows as a Cause of Microwave and X-Ray BurstsYu, SijieChen, BinReeves, Katharine K.Gary, Dale E.Musset, SophieFleishman, Gregory D.Nita, Gelu M.Glesener, LindsayDOI: info:10.3847/1538-4357/aba8a6v. 90017
Yu, Sijie, Chen, Bin, Reeves, Katharine K., Gary, Dale E., Musset, Sophie, Fleishman, Gregory D., Nita, Gelu M., and Glesener, Lindsay. 2020. "Magnetic Reconnection during the Post-impulsive Phase of a Long-duration Solar Flare: Bidirectional Outflows as a Cause of Microwave and X-Ray Bursts." The Astrophysical Journal 900:17.
ID: 157472
Type: article
Authors: Yu, Sijie; Chen, Bin; Reeves, Katharine K.; Gary, Dale E.; Musset, Sophie; Fleishman, Gregory D.; Nita, Gelu M.; Glesener, Lindsay
Abstract: Magnetic reconnection plays a crucial role in powering solar flares, production of energetic particles, and plasma heating. However, where the magnetic reconnections occur, how and where the released magnetic energy is transported, and how it is converted to other forms remain unclear. Here we report recurring bidirectional plasma outflows located within a large-scale plasma sheet observed in extreme-ultraviolet emission and scattered white light during the post-impulsive gradual phase of the X8.2 solar flare on 2017 September 10. Each of the bidirectional outflows originates in the plasma sheet from a discrete site, identified as a magnetic reconnection site. These reconnection sites reside at very low altitudes () above the top of the flare arcade, a distance only ) above the top of the flare arcade, a distance only . Each arrival of sunward outflows at the loop-top region appears to coincide with an impulsive microwave and X-ray burst dominated by a hot source (10-20 MK) at the loop top and a nonthermal microwave burst located in the loop-leg region. We propose that the reconnection outflows transport the magnetic energy released at localized magnetic reconnection sites outward in the form of kinetic energy flux and/or electromagnetic Poynting flux. The sunward-directed energy flux induces particle acceleration and plasma heating in the post-flare arcades, observed as the hot and nonthermal flare emissions.
Radio Spectroscopic Imaging of a Solar Flare Termination Shock: Split-band Feature as Evidence for Shock CompressionChen, BinShen, ChengcaiReeves, Katharine K.Guo, FanYu, SijieDOI: info:10.3847/1538-4357/ab3c58v. 88463
Chen, Bin, Shen, Chengcai, Reeves, Katharine K., Guo, Fan, and Yu, Sijie. 2019. "Radio Spectroscopic Imaging of a Solar Flare Termination Shock: Split-band Feature as Evidence for Shock Compression." The Astrophysical Journal 884:63.
ID: 154702
Type: article
Authors: Chen, Bin; Shen, Chengcai; Reeves, Katharine K.; Guo, Fan; Yu, Sijie
Abstract: Solar flare termination shocks have been suggested as one of the promising drivers for particle acceleration in solar flares, yet observational evidence remains rare. By utilizing radio dynamic spectroscopic imaging of decimetric stochastic spike bursts in an eruptive flare, Chen et al. found that the bursts form a dynamic surface-like feature located at the ending points of fast plasma downflows above the looptop, interpreted as a flare termination shock. One piece of observational evidence that strongly supports the termination shock interpretation is the occasional split of the emission band into two finer lanes in frequency, similar to the split-band feature seen in fast-coronal-shock-driven type II radio bursts. Here, we perform spatially, spectrally, and temporally resolved analysis of the split-band feature of the flare termination shock event. We find that the ensemble of the radio centroids from the two split-band lanes each outlines a nearly co-spatial surface. The high-frequency lane is located slightly below its low-frequency counterpart by ̃0.8 Mm, which strongly supports the shock-upstream-downstream interpretation. Under this scenario, the density compression ratio across the shock front can be inferred from the frequency split, which implies a shock with a Mach number of up to 2.0. Further, the spatiotemporal evolution of the density compression along the shock front agrees favorably with results from magnetohydrodynamics simulations. We conclude that the detailed variations of the shock compression ratio may be due to the impact of dynamic plasma structures in the reconnection outflows, which results in distortion of the shock front.
The Acceleration and Confinement of Energetic Electrons by a Termination Shock in a Magnetic Trap: An Explanation for Nonthermal Loop-top Sources during Solar FlaresKong, XiangliangGuo, FanShen, ChengcaiChen, BinChen, YaoMusset, SophieGlesener, LindsayPongkitiwanichakul, PeeraGiacalone, JoeDOI: info:10.3847/2041-8213/ab5f67v. 887L37
Kong, Xiangliang, Guo, Fan, Shen, Chengcai, Chen, Bin, Chen, Yao, Musset, Sophie, Glesener, Lindsay, Pongkitiwanichakul, Peera, and Giacalone, Joe. 2019. "The Acceleration and Confinement of Energetic Electrons by a Termination Shock in a Magnetic Trap: An Explanation for Nonthermal Loop-top Sources during Solar Flares." The Astrophysical Journal 887:L37.
ID: 154555
Type: article
Authors: Kong, Xiangliang; Guo, Fan; Shen, Chengcai; Chen, Bin; Chen, Yao; Musset, Sophie; Glesener, Lindsay; Pongkitiwanichakul, Peera; Giacalone, Joe
Abstract: Nonthermal loop-top sources in solar flares are the most prominent observational signatures that suggest energy release and particle acceleration in the solar corona. Although several scenarios for particle acceleration have been proposed, the origin of the loop-top sources remains unclear. Here we present a model that combines a large- scale magnetohydrodynamic simulation of a two-ribbon flare with a particle acceleration and transport model for investigating electron acceleration by a fast-mode termination shock (TS) at the loop top. Our model provides spatially resolved electron distribution that evolves in response to the dynamic flare geometry. We find a concave-downward magnetic structure located below the flare TS, induced by the fast reconnection downflows. It acts as a magnetic trap to confine the electrons at the loop top for an extended period of time. The electrons are energized significantly as they cross the shock front, and eventually build up a power-law energy spectrum extending to hundreds of kiloelectron volts. We suggest that this particle acceleration and transport scenario driven by a flare TS is a viable interpretation for the observed nonthermal loop-top sources.
Fungal Systematics and Evolution: FUSE 5Song, JieLiang, Jun-FengMehrabi-Koushki, MehdiKrisai-Greilhuber, IrmgardAli, BarkatBhatt, Vinod KumarCerna-Mendoza, AgustChen, BinChen, Zai-XiongChu, Hong-LongCorazon-Guivin, Mikeda Silva, Gladstone AlvesDe Kesel, AndréDima, BáDovana, FrancescoFarokhinejad, RezaFerisin, GulianoGuerrero-Abad, JuanGuo, TingHan, Li-HongIlyas, SobiaJusto, AlfredoKhalid, Abdul NasirKhodadadi-Pourarpanahi, SadighehLi, Tai-HuiLiu, ChaoLorenzini, MarilindaLu, Jun-KunMumtaz, Abdul SamadOehl, FritzPan, Xue-YuPapp, ViktorQian, WuRazaq, AbdulSemwal, Kamal C.Tang, Li-ZhouTian, Xue-LianVallejos-Tapullima, Adelavan der Merwe, Nicolaas A.Wang, Sheng-KunWang, Chao-QunYang, Rui-HengYu, FeiZapparoli, GiacomoZhang, MingAntonín, VladimirAptroot, AndréAslan, AliBanerjee, ArghyaChatterjee, SubrataDirks, Alden C.Ebrahimi, LeilaFotouhifar, Khalil-BerdiYoubert, GhostaKalinina, Lyudmila B.Karahan, DilaraLiu, JingyuMaiti, Mrinal KumarMookherjee, AbhirupNath, Partha SarathiPanja, BirendranathSaha, JayantaŠevčíková, HanaVoglmayr, HermannYazıcı, KenanHaelewaters, DannyDOI: info:10.12905/0380.sydowia71-2019-0141v. 71141–245
Song, Jie, Liang, Jun-Feng, Mehrabi-Koushki, Mehdi, Krisai-Greilhuber, Irmgard, Ali, Barkat, Bhatt, Vinod Kumar, Cerna-Mendoza, Agust, Chen, Bin, Chen, Zai-Xiong, Chu, Hong-Long, Corazon-Guivin, Mike, da Silva, Gladstone Alves, De Kesel, André, Dima, Bá, Dovana, Francesco, Farokhinejad, Reza, Ferisin, Guliano, Guerrero-Abad, Juan, Guo, Ting, Han, Li-Hong, Ilyas, Sobia, Justo, Alfredo, Khalid, Abdul Nasir, Khodadadi-Pourarpanahi, Sadigheh, Li, Tai-Hui et al. 2019. "Fungal Systematics and Evolution: FUSE 5." Sydowia 71:141– 245.
ID: 154293
Type: article
Authors: Song, Jie; Liang, Jun-Feng; Mehrabi-Koushki, Mehdi; Krisai-Greilhuber, Irmgard; Ali, Barkat; Bhatt, Vinod Kumar; Cerna-Mendoza, Agust; Chen, Bin; Chen, Zai-Xiong; Chu, Hong-Long; Corazon-Guivin, Mike; da Silva, Gladstone Alves; De Kesel, André; Dima, Bá; Dovana, Francesco; Farokhinejad, Reza; Ferisin, Guliano; Guerrero-Abad, Juan; Guo, Ting; Han, Li-Hong; Ilyas, Sobia; Justo, Alfredo; Khalid, Abdul Nasir; Khodadadi-Pourarpanahi, Sadigheh; Li, Tai-Hui; Liu, Chao; Lorenzini, Marilinda; Lu, Jun-Kun; Mumtaz, Abdul Samad; Oehl, Fritz; Pan, Xue-Yu; Papp, Viktor; Qian, Wu; Razaq, Abdul; Semwal, Kamal C.; Tang, Li-Zhou; Tian, Xue-Lian; Vallejos-Tapullima, Adela; van der Merwe, Nicolaas A.; Wang, Sheng-Kun; Wang, Chao-Qun; Yang, Rui-Heng; Yu, Fei; Zapparoli, Giacomo; Zhang, Ming; Antonín, Vladimir; Aptroot, André; Aslan, Ali; Banerjee, Arghya; Chatterjee, Subrata; Dirks, Alden C.; Ebrahimi, Leila; Fotouhifar, Khalil-Berdi; Youbert, Ghosta; Kalinina, Lyudmila B.; Karahan, Dilara; Liu, Jingyu; Maiti, Mrinal Kumar; Mookherjee, Abhirup; Nath, Partha Sarathi; Panja, Birendranath; Saha, Jayanta; Ševčíková, Hana; Voglmayr, Hermann; Yazıcı, Kenan; Haelewaters, Danny
Abstract: Thirteen new species are formally described: Cortinarius brunneocarpus from Pakistan, C. lilacinoarmillatus from India, Curvularia khuzestanica on Atriplex lentiformis from Iran, Gloeocantharellus neoechinosporus from China, Laboulbenia bernaliana on species of Apenes, Apristus, and Philophuga (Coleoptera, Carabidae) from Nicaragua and Panama, L. oioveliicola on Oiovelia machadoi (Hemiptera, Veliidae) from Brazil, L. termiticola on Macrotermes subhyalinus (Blattodea, Termitidae) from the DR Congo, Pluteus cutefractus from Slovenia, Rhizoglomus variabile from Peru, Russula phloginea from China, Stagonosporopsis flacciduvarum on Vitis vinifera from Italy, Strobilomyces huangshanensis from China, Uromyces klotzschianus on Rumex dentatus subsp. klotzschianus from Pakistan. The following new records are reported: Alternaria calendulae on Calendula officinalis from India; A. tenuissima on apple and quince fruits from Iran; Candelariella oleaginescens from Turkey; Didymella americana and D. calidophila on Vitis vinifera from Italy; Lasiodiplodia theobromae causing tip blight of Dianella tasmanica 'variegata' from India; Marasmiellus subpruinosus from Madeira, Portugal, new for Macaronesia and Africa; Mycena albidolilacea, M. tenuispinosa, and M. xantholeuca from Russia; Neonectria neomacrospora on Madhuca longifolia from India; Nothophoma quercina on Vitis vinifera from Italy; Plagiosphaera immersa on Urtica dioica from Austria; Rinodina sicula from Turkey; Sphaerosporium lignatile from Wisconsin, USA; and Verrucaria murina from Turkey. Multi-locus analysis of ITS, LSU, rpb1, tef1 sequences revealed that P. immersa, commonly classified within Gnomoniaceae (Diaporthales) or as Sordariomycetes incertae sedis, belongs to Magnaporthaceae (Magnaporthales). Analysis of a six-locus Ascomycota-wide dataset including SSU and LSU sequences of S. lignatile revealed that this species, currently in Ascomycota incertae sedis, belongs to Pyronemataceae (Pezizomycetes, Pezizales).
Magnetic Reconnection Null Points as the Origin of Semirelativistic Electron Beams in a Solar JetChen, BinYu, SijieBattaglia, MarinaFarid, SamaiyahSavcheva, AntoniaReeves, Katharine K.Krucker, SämBastian, T. S.Guo, FanTassev, SvetlinDOI: info:10.3847/1538-4357/aadb89v. 86662
Chen, Bin, Yu, Sijie, Battaglia, Marina, Farid, Samaiyah, Savcheva, Antonia, Reeves, Katharine K., Krucker, Säm, Bastian, T. S., Guo, Fan, and Tassev, Svetlin. 2018. "Magnetic Reconnection Null Points as the Origin of Semirelativistic Electron Beams in a Solar Jet." The Astrophysical Journal 866:62.
ID: 149383
Type: article
Authors: Chen, Bin; Yu, Sijie; Battaglia, Marina; Farid, Samaiyah; Savcheva, Antonia; Reeves, Katharine K.; Krucker, Säm; Bastian, T. S.; Guo, Fan; Tassev, Svetlin
Abstract: Magnetic reconnection, the central engine that powers explosive phenomena throughout the universe, is also perceived to be one of the principal mechanisms for accelerating particles to high energies. Although various signatures of magnetic reconnection have been frequently reported, observational evidence that links particle acceleration directly to the reconnection site has been rare, especially for space plasma environments currently inaccessible to in situ measurements. Here we utilize broadband radio dynamic imaging spectroscopy available from the Karl G. Jansky Very Large Array to observe decimetric type III radio bursts in a solar jet with high angular (∼20″), spectral (∼1%), and temporal resolution (50 ms). These observations allow us to derive detailed trajectories of semirelativistic (tens of keV) electron beams in the low solar corona with unprecedentedly high angular precision (2) in the low solar corona. The beam-diverging sites are located behind the erupting jet spire and above the closed arcades, coinciding with the presumed location of magnetic reconnection in the jet eruption picture supported by extreme ultraviolet/X-ray data and magnetic modeling. We interpret each beam-diverging site as a reconnection null point where multitudes of magnetic flux tubes join and reconnect. Our data suggest that the null points likely consist of a high level of density inhomogeneities possibly down to 10 km scales. These results, at least in the present case, strongly favor a reconnection-driven electron-acceleration scenario.
Broad Non-Gaussian Fe XXIV Line Profiles in the Impulsive Phase of the 2017 September 10 X8.3-class Flare Observed by Hinode/EISPolito, VanessaDudík, JaroslavKašparová, JanaDzifčáková, ElenaReeves, Katharine K.Testa, PaolaChen, BinDOI: info:10.3847/1538-4357/aad62dv. 86463
Polito, Vanessa, Dudík, Jaroslav, Kašparová, Jana, Dzifčáková, Elena, Reeves, Katharine K., Testa, Paola, and Chen, Bin. 2018. "Broad Non-Gaussian Fe XXIV Line Profiles in the Impulsive Phase of the 2017 September 10 X8.3-class Flare Observed by Hinode/EIS." The Astrophysical Journal 864:63.
ID: 149174
Type: article
Authors: Polito, Vanessa; Dudík, Jaroslav; Kašparová, Jana; Dzifčáková, Elena; Reeves, Katharine K.; Testa, Paola; Chen, Bin
Abstract: We analyze the spectra of high-temperature Fe XXIV lines observed by the Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) during the impulsive phase of the X8.3-class flare on 2017 September 10. The line profiles are broad, show pronounced wings, and clearly depart from a single-Gaussian shape. The lines can be well fitted with κ distributions, with values of κ varying between ≈1.7 and 3. The regions where we observe the non-Gaussian profiles coincide with the location of high-energy (≈100–300 keV) hard X-ray (HXR) sources observed by RHESSI, suggesting the presence of particle acceleration or turbulence, also confirmed by the observations of nonthermal microwave sources with the Expanded Owens Valley Solar Array at and above the HXR loop-top source. We also investigate the effect of taking into account κ distributions in the temperature diagnostics based on the ratio of the Fe XXIII λ263.76 and Fe XXIV λ255.1 EIS lines. We found that these lines can be formed at much higher temperatures than expected (up to log(T[K]) ≈ 7.8) if departures from Maxwellian distributions are taken into account. Although larger line widths are expected because of these higher formation temperatures, the observed line widths still imply nonthermal broadening in excess of 200 km s‑1. The nonthermal broadening related to HXR emission is better interpreted by turbulence than by chromospheric evaporation.
The Dynamical Behavior of Reconnection-driven Termination Shocks in Solar Flares: Magnetohydrodynamic SimulationsShen, ChengcaiKong, XiangliangGuo, FanRaymond, John C.Chen, BinDOI: info:10.3847/1538-4357/aaeed3v. 869116
Shen, Chengcai, Kong, Xiangliang, Guo, Fan, Raymond, John C., and Chen, Bin. 2018. "The Dynamical Behavior of Reconnection-driven Termination Shocks in Solar Flares: Magnetohydrodynamic Simulations." The Astrophysical Journal 869:116.
ID: 150219
Type: article
Authors: Shen, Chengcai; Kong, Xiangliang; Guo, Fan; Raymond, John C.; Chen, Bin
Abstract: In eruptive solar flares, termination shocks (TSs), formed when high-speed reconnection outflows collide with closed dense flaring loops, are believed to be one of the possible candidates for plasma heating and particle acceleration. In this work, we perform resistive magnetohydrodynamic simulations in a classic Kopp–Pneuman flare configuration to study the formation and evolution of TSs, and we analyze in detail the dynamic features of TSs and variations of the shock strength in space and time. This research focuses on the fast-reconnection phase when plasmoids form and produce small-scale structures inside the flare current sheet. It is found that the TS emerges once the downward outflow colliding with closed magnetic loops becomes supermagnetosonic and immediately becomes highly dynamical. The morphology of a TS can be flat, oblique, or curved depending on the detailed interactions between the outflows/plasmoids and the highly dynamic plasma in the loop-top region. The TS becomes weaker when a plasmoid is crossing through, or may even be destroyed by well-developed plasmoids and then reconstructed above the plasmoids. We also perform detailed statistical analysis on important physical quantities along and across the shock front. The density and temperature ratios range from 1 to 3 across the TS front, and the pressure ratio typically has larger values up to 10. We show that weak guide fields do not strongly affect the Mach number and compression ratios, and the TS length becomes slightly larger in the case with thermal conduction.
The First Focused Hard X-ray Images of the Sun with NuSTARGrefenstette, Brian W.Glesener, LindsayKrucker, SämHudson, HughHannah, Iain G.Smith, David M.Vogel, Julia K.White, Stephen M.Madsen, Kristin K.Marsh, Andrew J.Caspi, AmirChen, BinShih, AlbertKuhar, MatejBoggs, Steven E.Christensen, Finn E.Craig, William W.Forster, KarlHailey, Charles J.Harrison, Fiona A.Miyasaka, HiromasaStern, DanielZhang, William W.DOI: info:10.3847/0004-637X/826/1/20v. 82620
Grefenstette, Brian W., Glesener, Lindsay, Krucker, Säm, Hudson, Hugh, Hannah, Iain G., Smith, David M., Vogel, Julia K., White, Stephen M., Madsen, Kristin K., Marsh, Andrew J., Caspi, Amir, Chen, Bin, Shih, Albert, Kuhar, Matej, Boggs, Steven E., Christensen, Finn E., Craig, William W., Forster, Karl, Hailey, Charles J., Harrison, Fiona A., Miyasaka, Hiromasa, Stern, Daniel, and Zhang, William W. 2016. "The First Focused Hard X-ray Images of the Sun with NuSTAR." The Astrophysical Journal 826:20.
ID: 140228
Type: article
Authors: Grefenstette, Brian W.; Glesener, Lindsay; Krucker, Säm; Hudson, Hugh; Hannah, Iain G.; Smith, David M.; Vogel, Julia K.; White, Stephen M.; Madsen, Kristin K.; Marsh, Andrew J.; Caspi, Amir; Chen, Bin; Shih, Albert; Kuhar, Matej; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Forster, Karl; Hailey, Charles J.; Harrison, Fiona A.; Miyasaka, Hiromasa; Stern, Daniel; Zhang, William W.
Abstract: We present results from the the first campaign of dedicated solar observations undertaken by the Nuclear Spectroscopic Telescope ARray (NuSTAR) hard X-ray (HXR) telescope. Designed as an astrophysics mission, NuSTAR nonetheless has the capability of directly imaging the Sun at HXR energies (>3 keV) with an increase in sensitivity of at least two magnitude compared to current non-focusing telescopes. In this paper we describe the scientific areas where NuSTAR will make major improvements on existing solar measurements. We report on the techniques used to observe the Sun with NuSTAR, their limitations and complications, and the procedures developed to optimize solar data quality derived from our experience with the initial solar observations. These first observations are briefly described, including the measurement of the Fe K-shell lines in a decaying X-class flare, HXR emission from high in the solar corona, and full-disk HXR images of the Sun.
Global Sausage Oscillation of Solar Flare Loops Detected by the Interface Region Imaging SpectrographTian, HuiYoung, Peter R.Reeves, Katharine K.Wang, TongjiangAntolin, PatrickChen, BinHe, JiansenDOI: info:10.3847/2041-8205/823/1/L16v. 823L16
Tian, Hui, Young, Peter R., Reeves, Katharine K., Wang, Tongjiang, Antolin, Patrick, Chen, Bin, and He, Jiansen. 2016. "Global Sausage Oscillation of Solar Flare Loops Detected by the Interface Region Imaging Spectrograph." Astrophysical Journal Letters 823:L16.
ID: 139793
Type: article
Authors: Tian, Hui; Young, Peter R.; Reeves, Katharine K.; Wang, Tongjiang; Antolin, Patrick; Chen, Bin; He, Jiansen
Abstract: An observation from the Interface Region Imaging Spectrograph reveals coherent oscillations in the loops of an M1.6 flare on 2015 March 12. Both the intensity and Doppler shift of Fe xxi 1354.08 Å show clear oscillations with a period of ~25 s. Remarkably similar oscillations were also detected in the soft X-ray flux recorded by the Geostationary Operational Environmental Satellites (GOES). With an estimated phase speed of ~2420 km s-1 and a derived electron density of at least 5.4 × 1010 cm-3, the observed short-period oscillation is most likely the global fast sausage mode of a hot flare loop. We find a phase shift of ~?/2 (1/4 period) between the Doppler shift oscillation and the intensity/GOES oscillations, which is consistent with a recent forward modeling study of the sausage mode. The observed oscillation requires a density contrast between the flare loop and coronal background of a factor >=42. The estimated phase speed of the global mode provides a lower limit of the Alfvén speed outside the flare loop. We also find an increase of the oscillation period, which might be caused by the separation of the loop footpoints with time.
Resolving the Fan-spine Reconnection Geometry of a Small-scale Chromospheric Jet Event with the New Solar TelescopeZeng, ZhichengChen, BinJi, HaishengGoode, Philip R.Cao, WendaDOI: info:10.3847/2041-8205/819/1/L3v. 819L3
Zeng, Zhicheng, Chen, Bin, Ji, Haisheng, Goode, Philip R., and Cao, Wenda. 2016. "Resolving the Fan-spine Reconnection Geometry of a Small-scale Chromospheric Jet Event with the New Solar Telescope." Astrophysical Journal Letters 819:L3.
ID: 139327
Type: article
Authors: Zeng, Zhicheng; Chen, Bin; Ji, Haisheng; Goode, Philip R.; Cao, Wenda
Abstract: Jets are ubiquitously present in both quiet and active regions on the Sun. They are widely believed to be driven by magnetic reconnection. A fan-spine structure has been frequently reported in some coronal jets and flares, and has been regarded as a signature of ongoing magnetic reconnection in a topology consisting of a magnetic null connected by a fan-like separatrix surface and a spine. However, for small-scale chromospheric jets, clear evidence of such structures is rather rare, although it has been implied in earlier works that showed an inverted-Y-shaped feature. Here we report high-resolution (0.?16) observations of a small-scale chromospheric jet obtained by the New Solar Telescope (NST) using 10830 Å filtergrams. Bi-directional flows were observed across the separatrix regions in the 10830 Å images, suggesting that the jet was produced due to magnetic reconnection. At the base of the jet, a fan-spine structure was clearly resolved by the NST, including the spine and the fan-like surface, as well as the loops before and after the reconnection. A major part of this fan-spine structure, with the exception of its bright footpoints and part of the base arc, was invisible in the extreme ultraviolet and soft X-ray images (observed by the Atmosphere Imaging Assembly and the X-Ray Telescope, respectively), indicating that the reconnection occurred in the upper chromosphere. Our observations suggest that the evolution of this chromospheric jet is consistent with a two-step reconnection scenario proposed by Török et al.
Particle acceleration by a solar flare termination shockChen, BinBastian, Timothy S.Shen, ChengcaiGary, Dale E.Krucker, SämGlesener, LindsayDOI: info:10.1126/science.aac8467v. 3501238–1242
Chen, Bin, Bastian, Timothy S., Shen, Chengcai, Gary, Dale E., Krucker, Säm, and Glesener, Lindsay. 2015. "Particle acceleration by a solar flare termination shock." Science 350:1238– 1242.
ID: 138562
Type: article
Authors: Chen, Bin; Bastian, Timothy S.; Shen, Chengcai; Gary, Dale E.; Krucker, Säm; Glesener, Lindsay
Abstract: Solar flares—the most powerful explosions in the solar system—are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of solar flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a solar flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. The observed properties of the shock are well reproduced by simulations. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares.
Temporal Evolution of Chromospheric Evaporation: Case Studies of the M1.1 Flare on 2014 September 6 and X1.6 Flare on 2014 September 10Tian, HuiYoung, Peter R.Reeves, Katharine K.Chen, BinLiu, WeiMcKillop, SeanDOI: info:10.1088/0004-637X/811/2/139v. 811139
Tian, Hui, Young, Peter R., Reeves, Katharine K., Chen, Bin, Liu, Wei, and McKillop, Sean. 2015. "Temporal Evolution of Chromospheric Evaporation: Case Studies of the M1.1 Flare on 2014 September 6 and X1.6 Flare on 2014 September 10." The Astrophysical Journal 811:139.
ID: 140590
Type: article
Authors: Tian, Hui; Young, Peter R.; Reeves, Katharine K.; Chen, Bin; Liu, Wei; McKillop, Sean
Abstract: With observations from the Interface Region Imaging Spectrograph, we track the complete evolution of ~11 MK evaporation flows in an M1.1 flare on 2014 September 6 and an X1.6 flare on 2014 September 10. These hot flows, as indicated by the blueshifted Fe xxi 1354.08 Å line, evolve smoothly with a velocity decreasing exponentially from ~200 km s-1 to almost stationary within a few minutes. We find a good correlation between the flow velocity and energy deposition rate as represented by the hard X-ray flux observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager, or time derivative of the soft X-ray flux observed with the Geostationary Operational Environmental Satellites and the HINODE X-ray Telescope, which is in general agreement with models of nonthermal electron heating. The maximum blueshift of Fe xxi appears approximately at the same time as or slightly after the impulsive enhancement of the ultraviolet continuum and the Mg ii 2798.8 Å line emission, demonstrating that the evaporation flow is closely related to heating of the lower chromosphere. Finally, while the hot Fe xxi 1354.08 Å line is entirely blueshifted with no obvious rest component, cool chromospheric and transition region lines like Si iv 1402.77 Å are often not entirely redshifted but just reveal an obvious red wing enhancement at the ribbons, suggesting that the speed of chromospheric condensation might be larger than previously thought.
Direct Evidence of an Eruptive, Filament-hosting Magnetic Flux Rope Leading to a Fast Solar Coronal Mass EjectionChen, BinBastian, T. S.Gary, D. E.DOI: info:10.1088/0004-637X/794/2/149v. 794149
Chen, Bin, Bastian, T. S., and Gary, D. E. 2014. "Direct Evidence of an Eruptive, Filament-hosting Magnetic Flux Rope Leading to a Fast Solar Coronal Mass Ejection." The Astrophysical Journal 794:149.
ID: 131099
Type: article
Authors: Chen, Bin; Bastian, T. S.; Gary, D. E.
Abstract: Magnetic flux ropes (MFRs) are believed to be at the heart of solar coronal mass ejections (CMEs). A well-known example is the prominence cavity in the low corona that sometimes makes up a three-part white-light (WL) CME upon its eruption. Such a system, which is usually observed in quiet-Sun regions, has long been suggested to be the manifestation of an MFR with relatively cool filament material collecting near its bottom. However, observational evidence of eruptive, filament-hosting MFR systems has been elusive for those originating in active regions. By utilizing multi-passband extreme-ultraviolet (EUV) observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly, we present direct evidence of an eruptive MFR in the low corona that exhibits a hot envelope and a cooler core; the latter is likely the upper part of a filament that undergoes a partial eruption, which is later observed in the upper corona as the coiled kernel of a fast, WL CME. This MFR-like structure exists more than 1 hr prior to its eruption, and displays successive stages of dynamical evolution, in which both ideal and non-ideal physical processes may be involved. The timing of the MFR kinematics is found to be well correlated with the energy release of the associated long-duration C1.9 flare. We suggest that the long-duration flare is the result of prolonged energy release associated with the vertical current sheet induced by the erupting MFR.
Imaging and Spectroscopic Observations of Magnetic Reconnection and Chromospheric Evaporation in a Solar FlareTian, HuiLi, GangReeves, Katharine K.Raymond, John C.Guo, FanLiu, WeiChen, BinMurphy, Nicholas A.DOI: info:10.1088/2041-8205/797/2/L14v. 797L14
Tian, Hui, Li, Gang, Reeves, Katharine K., Raymond, John C., Guo, Fan, Liu, Wei, Chen, Bin, and Murphy, Nicholas A. 2014. "Imaging and Spectroscopic Observations of Magnetic Reconnection and Chromospheric Evaporation in a Solar Flare." Astrophysical Journal Letters 797:L14.
ID: 133417
Type: article
Authors: Tian, Hui; Li, Gang; Reeves, Katharine K.; Raymond, John C.; Guo, Fan; Liu, Wei; Chen, Bin; Murphy, Nicholas A.
Abstract: Magnetic reconnection is believed to be the dominant energy release mechanism in solar flares. The standard flare model predicts both downward and upward outflow plasmas with speeds close to the coronal Alfvén speed. Yet, spectroscopic observations of such outflows, especially the downflows, are extremely rare. With observations of the newly launched Interface Region Imaging Spectrograph (IRIS), we report the detection of a greatly redshifted (~125 km s-1 along the line of sight) Fe XXI 1354.08 Å emission line with a ~100 km s-1 nonthermal width at the reconnection site of a flare. The redshifted Fe XXI feature coincides spatially with the loop-top X-ray source observed by RHESSI. We interpret this large redshift as the signature of downward-moving reconnection outflow/hot retracting loops. Imaging observations from both IRIS and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory also reveal the eruption and reconnection processes. Fast downward-propagating blobs along these loops are also found from cool emission lines (e.g., Si IV, O IV, C II, Mg II) and images of AIA and IRIS. Furthermore, the entire Fe XXI line is blueshifted by ~260 km s-1 at the loop footpoints, where the cool lines mentioned above all exhibit obvious redshift, a result that is consistent with the scenario of chromospheric evaporation induced by downward-propagating nonthermal electrons from the reconnection site.