Systematic non-thermal velocity increase preceding soft X-ray flare onset: A large-scale Hinode/EIS study
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| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866912599777476608 |
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| author | To, Andy S. H. Burden, Abigail Baker, Deborah Eklund, Henrik Brooks, David H. Hayes, Laura A. Martínez-Sykora, Juan Testa, Paola Reep, Jeffrey Janvier, Miho Imada, Shinsuke Camero, Julio Hernandez Long, David M. Mihailescu, Teodora Weberg, Micah J. |
| author_facet | To, Andy S. H. Burden, Abigail Baker, Deborah Eklund, Henrik Brooks, David H. Hayes, Laura A. Martínez-Sykora, Juan Testa, Paola Reep, Jeffrey Janvier, Miho Imada, Shinsuke Camero, Julio Hernandez Long, David M. Mihailescu, Teodora Weberg, Micah J. |
| contents | Non-thermal velocities, derived from spectral line broadening, can provide crucial insights into plasma dynamics before and during solar flares. To systematically study the pre-flare phase, we constructed a Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) flare catalog of 1,449 flares from 2011--2024. This enabled a large-scale analysis of flare loop footpoint non-thermal velocity evolution across different flare magnitudes (C, M, X-classes). Analyzing Fe VIII--Fe XXIV emission lines formed at $\log(T/K) \sim 5.7-7.3$ with piecewise linear fits in the pre-flare period, we find that non-thermal velocities consistently increase 4--25 minutes before GOES soft X-ray start in C and M-class flares. Onset timing patterns vary with flare magnitude: smaller flares show temperature-dependent progression, while larger flares exhibit more compressed, near-simultaneous onsets across temperatures. While our limited X-class sample ($N=18$) also show onset before GOES, larger statistics are needed to confirm its behavior. M-class flares show a systematic precursor non-thermal velocity onset $\sim$30--60 minutes before GOES peak. In a subset of M-class flares (2011--2018), CME-associated events show earlier and more uniform precursor onsets (45--74 minutes before peak) than non-CME events, of which only some lines display a precursor, suggesting a strong link between extended pre-flare non-thermal broadening and successful eruptions. This large scale study establishes pre-flare non-thermal velocity increase at footpoints as a common precursor observable before any X-ray signature. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_15921 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Systematic non-thermal velocity increase preceding soft X-ray flare onset: A large-scale Hinode/EIS study To, Andy S. H. Burden, Abigail Baker, Deborah Eklund, Henrik Brooks, David H. Hayes, Laura A. Martínez-Sykora, Juan Testa, Paola Reep, Jeffrey Janvier, Miho Imada, Shinsuke Camero, Julio Hernandez Long, David M. Mihailescu, Teodora Weberg, Micah J. Solar and Stellar Astrophysics Non-thermal velocities, derived from spectral line broadening, can provide crucial insights into plasma dynamics before and during solar flares. To systematically study the pre-flare phase, we constructed a Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) flare catalog of 1,449 flares from 2011--2024. This enabled a large-scale analysis of flare loop footpoint non-thermal velocity evolution across different flare magnitudes (C, M, X-classes). Analyzing Fe VIII--Fe XXIV emission lines formed at $\log(T/K) \sim 5.7-7.3$ with piecewise linear fits in the pre-flare period, we find that non-thermal velocities consistently increase 4--25 minutes before GOES soft X-ray start in C and M-class flares. Onset timing patterns vary with flare magnitude: smaller flares show temperature-dependent progression, while larger flares exhibit more compressed, near-simultaneous onsets across temperatures. While our limited X-class sample ($N=18$) also show onset before GOES, larger statistics are needed to confirm its behavior. M-class flares show a systematic precursor non-thermal velocity onset $\sim$30--60 minutes before GOES peak. In a subset of M-class flares (2011--2018), CME-associated events show earlier and more uniform precursor onsets (45--74 minutes before peak) than non-CME events, of which only some lines display a precursor, suggesting a strong link between extended pre-flare non-thermal broadening and successful eruptions. This large scale study establishes pre-flare non-thermal velocity increase at footpoints as a common precursor observable before any X-ray signature. |
| title | Systematic non-thermal velocity increase preceding soft X-ray flare onset: A large-scale Hinode/EIS study |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2506.15921 |