IRIS Nugget
Welcome to the IRIS Science Nuggets: highlights of recent IRIS scientific results for the solar physics community.
{"id":"pod_polito_vanessa_2024-09-03T16:57:57.431Z","submitter":"","author":"William Ashfield IV [1,2], Vanessa Polito [2,3], Sijie Yu [4], Hannah Collier [5,6], Laura Hayes [7]","status":"published","creation-date":"2024-09-03T16:57:57.465Z","last-modified-date":"2024-09-13T18:09:01.397Z","credit":"[1] Bay Area Environmental Research Institute, [2] Lockheed Martin Solar and Astrophysics Laboratory, [3] Oregon State University, Department of Physics, [4] Center for Solar-Terrestrial Research, New Jersey Institute of Technology, [5] University of Applied Sciences and Arts Northwestern Switzerland, [6] ETH Zürich, [7] European Space Agency","title":"Non-thermal Observations of a Flare Loop-top using IRIS Fe XXI: Implications for Turbulence and Electron Acceleration","contentBlocks":[{"type":"text","text":"The%20excess%20broadening%20of%20high-temperature%20Fe%20spectra%20along%20arcade%20loops%20is%20a%20common%20feature%20of%20solar%20flares.%20Widely%20thought%20to%20be%20a%20signature%20of%20MHD%20turbulence%2C%20these%20observations%20allow%20us%20to%20probe%20the%20dynamics%20of%20turbulence%20as%20it%20pertains%20to%20flare%20energy%20release.%20This%20idea%20was%20most%20recently%20explored%20by%20Shen%20et%20al.%202023%2C%20who%20found%20turbulent%20bulk%20plasma%20flows%20in%20the%20loop-top%20and%20cusp%20regions%20to%20be%20responsible%20for%20the%20non-thermal%20broadening%20of%20the%20Fe%20XXI%20emission%20line.%20%0A%0ATurbulence%20in%20these%20regions%20is%20also%20a%20candidate%20mechanism%20for%20particle%20acceleration%20%28Larosa%20%26amp%3B%20Moore%201993%29.%20Kontar%20et%20al.%202017%20used%20the%20decay%20of%20non-thermal%20broadening%20in%20EIS%20Fe%20lines%20as%20a%20proxy%20for%20turbulent%20energy%20dissipation%2C%20and%20found%20the%20rate%20of%20kinetic%20energy%20loss%20to%20be%20consistent%20with%20the%20power%20of%20non-thermal%20electron%20deposition%20in%20the%20chromosphere.%20Despite%20this%20progress%2C%20the%20decay%20of%20non-thermal%20broadenings%20and%20their%20subsequent%20connection%20to%20the%20acceleration%20site%20of%20non-thermal%20electrons%20remains%20largely%20unexplored.%0A%0AIn%20this%20work%20%28Ashfield%20et%20al.%202024%29%2C%20we%20analyzed%20non-thermal%20signatures%20of%20a%20X1.3%20class%20flare.%20Figure%201%20shows%20the%20evolution%20of%20IRIS%20Fe%20XXI%2C%20which%20emanated%20from%20the%20loop%20arcade%20located%20between%20the%20two%20flare%20ribbons%20and%20had%20significant%20excess%20line%20broadening.%20The%20broadening%20was%20also%20observed%20to%20decay%20over%20time%20at%20two%20different%20periods%2C%20beginning%20at%20the%20onset%20of%20loop-top%20emission%20at%2017%3A33%3A25%20and%20before%20peak%20line%20emission."},{"type":"image","file":"","url":"nuggetvideos/2024/09/03/pod_polito_vanessa_2024-09-03T16%3A57%3A57.431Z/fig1.png","hash":"5b134d8cbe21e4e4f9754223a92f4033","mimeType":"image/png","caption":"Figure%201.%20Evolution%20of%20the%20flare%20arcade%20in%20SJI%201330%20%26Aring%3B%20at%20two%20times%20-%20%28a%29%20and%20%28b%29%20-%20showing%20the%20location%20of%20the%20Fe%20XXI%20emission%20along%20the%20SG%20slit%20%28colored%20line%29.%20%28c%29%20IRIS%20detector%20image%20of%20the%20O%20I%20channel%20%28left%29%2C%20illustrating%20the%20dynamic%20binning%20routine%2C%20with%20the%20resulting%20binned%20spectra%20%28black%29%20and%20best%20Gaussian%20fit%20%28red%29%20shown%20on%20the%20right.%20%28d%29%20Time-distance%20stack%20plots%20of%20Fe%20XXI%20spectral%20line%20parameters%3A%20Intensity%20%28top%29%2C%20Doppler%20Velocity%20%28middle%29%2C%20and%20non-thermal%20velocity%20%28bottom%29."},{"type":"text","text":"In%20the%20first%20instance%20of%20Fe%20XXI%20emission%2C%20the%20O%20I%20detector%20image%20showed%20a%20well-resolved%2C%203%20arcsec%20loop-top%20structure%20at%20IRIS%20high%20spatial%20resolution%20%28Figure%201-c%29.%20This%20structure%2C%20determined%20from%20a%20routine%20that%20identified%20strong%20Fe%20XXI%20signals%2C%20contained%20non-thermal%20velocities%20upwards%20of%2065%20km%2Fs.%20Confirming%20the%20LT%20emission%20from%20a%20well-resolved%20structure%20not%20only%20indicates%20the%20presence%20of%20plasma%20turbulence%20but%20also%20challenges%20earlier%20works%20using%20lower-resolution%20spectrometers%2C%20where%20flare%20emissions%20might%20have%20been%20interpreted%20as%20a%20superposition%20of%20flows%20from%20different%20macroscopic%20locations%20along%20the%20flare%20arcade%20and%20LOS%20%28e.g.%20Stores%202021%29.%20%0A%0AAdditional%20non-thermal%20signatures%20in%20this%20flare%20were%20found%20using%20EOVSA%20%28Gary%20et%20al.%202018%29%20and%20STIX%20%28Krucker%20et%20al.%202020%29.%20Figure%202%20shows%20the%20location%20of%20microwaves%20and%20X-rays%20during%20the%20flare.%20Notably%2C%20the%20microwave%20emission%20was%20co-spatial%20and%20co-temporal%20with%20the%20Fe%20XXI%20emission.%20Spectral%20analysis%20of%20the%20compact%20sources%20also%20indicated%20a%20substantial%20non-thermal%20electron%20population%2C%20with%20a%20ratio%20of%20non-thermal%20to%20thermal%20electrons%20reaching%2035%25%20%28Dulk%20%26amp%3B%20Marsh%201982%29.%20This%20high%20percentage%20indicates%20an%20efficient%20electron%20acceleration%20mechanism%20at%20work%2C%20and%20places%20plasma%20turbulence%20measured%20with%20IRIS%20in%20the%20vicinity%20of%20these%20non-thermal%20electrons%20at%20the%20flare%20loop-top."},{"type":"image","file":"","url":"nuggetvideos/2024/09/03/pod_polito_vanessa_2024-09-03T16%3A57%3A57.431Z/fig2.png","hash":"5fa40c2c60c6450c5b0481dccfe22ec8","mimeType":"image/png","caption":"Figure%202.%20Spatially%20resolved%20EOVSA%20MW%20sources%20overlaid%20on%20AIA%201600%26Aring%3B%20images%20with%2070%25%20contours%20%28grey%29%20and%20SG%20slit%20%28red-dashed%29%20-%20%28a%29%20and%20%28b%29.%20%28c%29%20Reconstructed%20STIX%20SXR%20%28yellow%29%20and%20HXR%20%28red%29%20images%20overlaid%20on%20reprojected%20AIA%201600%26Aring%3B%20images%20with%2070%25%20contours%20%28orange%29%20from%20the%20viewpoint%20of%20Solar%20Orbiter.%20%28d%29%20Schematic%20diagram%20showing%20the%20interpreted%20locations%20of%20the%20different%20observations%20along%20the%20line-of-sight%20%28LOS%29%20as%20they%20pertain%20to%20the%20standard%20flare%20model.%20Microwave%20%28MW%29%20sources%20are%20confined%20to%20the%20closed%2C%20reconnected%20post-flare%20loops%2C%20which%20trace%20out%20the%20northern%20half%20of%20the%20loop-like%20structure.%20High-frequency%20sources%20%28yellow%29%20stem%20from%20the%20northern%20ribbon%2C%20while%20the%20low-frequency%20sources%20%28blue%29%20emanate%20from%20the%20LT%2FCusp%20region.%20The%20hard%20X-ray%20%28HXR%29%20source%20marks%20the%20location%20of%20the%20southern%20footprint%2C%20arising%20from%20the%20precipitation%20of%20accelerated%20electrons.%20Lying%20above%20the%20MWs%20in%20the%20LT%2FCusp%20region%2C%20near%20the%20location%20where%20the%20current%20sheet%20meets%20the%20arcade%2C%20is%20the%20Fe%20XXI%20non-thermal%20broadening%20detected%20along%20the%20IRIS%20SG%20slit."},{"type":"text","text":"Following%20methodologies%20from%20Kontar%20et%20al.%20%282017%29%2C%20we%20further%20explored%20the%20connection%20between%20turbulence%20and%20electron%20acceleration%20by%20comparing%20the%20decay%20in%20Fe%20XXI%20non-thermal%20broadening%20to%20the%20time-integrated%20non-thermal%20electron%20power%20deposited%20in%20the%20chromosphere%2C%20as%20inferred%20from%20STIX%20hard%20X-rays.%20Assuming%20the%20decay%20in%20non-thermal%20broadening%20is%20indicative%20of%20energy%20dissipation%20via%20a%20turbulent%20cascade%2C%20we%20converted%20the%20non-thermal%20velocities%20into%20turbulent%20kinetic%20energies%20using%20estimates%20for%20the%20electron%20number%20density%20and%20a%20coronal%20volume%20of%20the%20loop-top%20%28Figure%203%29."},{"type":"image","file":"","url":"nuggetvideos/2024/09/03/pod_polito_vanessa_2024-09-03T16%3A57%3A57.431Z/fig3.png","hash":"610123eb0979fdd8cbab08f82ac7daef","mimeType":"image/png","caption":"Figure%203.%20%28a%29%20Time%20series%20of%20Fe%20XXI%20spectral%20line%20parameters%20from%20the%20dynamic%20binning%20routine%20over%20the%20initial%20signal%2C%20with%20the%20best%20linear%20fit%20to%20the%20non-thermal%20velocity%20%28red-dashed%20line%29.%20%28b%29%20Time%20series%20of%20the%20turbulent%20kinetic%20energy%20inferred%20from%20IRIS%20Fe%20XXI%20non-thermal%20broadening%20during%20the%20initial%20signal%20%28orange%29%20and%20the%20corresponding%20time-integrated%20non-thermal%20power%20from%20STIX%20HXR%20emission%20during%20the%20second%20energy%20phase%20%28purple%29."},{"type":"text","text":"We%20found%20the%20peak%20in%20the%20turbulent%20kinetic%20energy%20%282.8%20%26plusmn%3B%200.8%20%26times%3B%2010%3Csup%3E28%3C%2Fsup%3E%20erg%29%20matched%20the%20peak%20integrated%20electron%20power%20from%20STIX%20%282.4%20%26plusmn%3B%200.4%20%26times%3B%2010%3Csup%3E28%3C%2Fsup%3E%20erg%29.%20The%20decay%20between%20the%20inferred%20kinetic%20energy%20and%20non-thermal%20electron%20power%20was%20also%20consistent%20over%20time.%20Together%2C%20the%20agreement%20between%20the%20two%20energies%20suggests%20a%20relationship%20between%20the%20dissipation%20of%20turbulent%20energy%20and%20the%20acceleration%20of%20non-thermal%20electrons.%20When%20compared%20to%20the%20non-thermal%20energy%20density%20inferred%20from%20the%20microwave%20sources%2C%20however%2C%20the%20kinetic%20energy%20density%20was%20much%20lower.%20%20This%20discrepancy%2C%20first%20seen%20in%20Fleishman%20et%20al.%20%282020%29%2C%20supports%20the%20idea%20of%20a%20vertical%20variation%20in%20the%20non-thermal%20energy%20density%20across%20the%20flare%20arcade%2C%20where%20the%20formation%20region%20of%20Fe%20XXI%20belongs%20to%20a%20region%20of%20lesser%20non-thermal%20energy%20density%2C%20possibly%20higher%20in%20the%20solar%20corona%20than%20the%20underlying%20MW%20emission%2C%20as%20summarised%20in%20the%20cartoon%20in%20Figure%202-d.%0A%0A%0AThe%20interconnection%20between%20signatures%20in%20this%20work%20offers%20a%20unique%20observation%20that%20contributes%20to%20a%20deeper%20understanding%20of%20non-thermal%20processes%20in%20solar%20flares.%20Between%20the%20presence%20of%20non-thermal%20electrons%20in%20the%20loop-top%20inferred%20from%20EOVSA%2C%20the%20co-spatiotemporal%20IRIS%20Fe%20XXI%20non-thermal%20broadening%20implying%20plasma%20turbulence%2C%20and%20the%20subsequent%20rate%20of%20turbulent%20energy%20dissipation%20that%20is%20consistent%20with%20the%20deposited%20electron%20power%20measured%20with%20STIX%2C%20our%20analysis%20could%20be%20indicative%20of%20a%20stochastic%20acceleration%20mechanism%20at%20play."}],"references":["<a 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P. 2021, ApJ, 923, 40</a>",""],"pubDate":"2024-09-13T18:09:26.875Z"}