Strong Photospheric Heating Indicated by Fe I 6173 {\AA} Line Emission During White-Light Solar Flares
Between 2017 and 2024, the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory has observed several white-light solar flares. Notably, for the X9.3 flare of September 6, 2017, HMI spectro-polarimetric observations reveal one or more locations within the umbra of the associa...
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Main Authors | , , , , |
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Format | Journal Article |
Language | English |
Published |
09.10.2024
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Subjects | |
Online Access | Get full text |
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Summary: | Between 2017 and 2024, the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamics Observatory has observed several white-light solar flares.
Notably, for the X9.3 flare of September 6, 2017, HMI spectro-polarimetric
observations reveal one or more locations within the umbra of the associated
active region where the Fe I 6173 {\AA} line goes into full emission,
indicating significant heating of the photosphere and lower chromosphere. For
these flares, we performed a spectro-polarimetric analysis at the
aforementioned locations using HMI 90s cadence Stokes data. At the Fe I
emission locations, line-core emission is observed to last for a single 90 s
frame and is either concurrent with or followed by increases in the line
continuum intensity lasting 90 to 180 seconds. This is followed by a smooth
decay to pre-flare conditions over the next three to twenty minutes. For most
locations, permanent changes to the Stokes Q, U, and/or V profiles were
observed, indicating long-lasting non-transient changes to the photospheric
magnetic field. These emissions coincided with local maxima in hard X-ray
emission observed by the Konus instrument onboard the Wind spacecraft, as well
as local maxima in the time derivative of soft X-ray emission observed by GOES
satellites. Comparison of the Fe I 6173 {\AA} line profile synthesis for the
ad-hoc heating of the initial empirical VAL-S umbra model and quiescent Sun
(VAL-C-like) model indicates that the Fe I 6173 {\AA} line emission in the
white-light flare kernels could be explained by the strong heating of initially
cool photospheric regions. |
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DOI: | 10.48550/arxiv.2410.07440 |