An Explanation of Remarkable Emission Line Profiles In Post-Flare Coronal Rain

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Tuesday, August 8, 2017

We study broad red-shifted emission in chromospheric and transition region lines that appears to correspond to a form of post-flare coronal rain.

Intensity profiles of the Mg II h and k lines image
Intensity profiles of the Mg II h and k lines before during and after the X2.1 flare of 11 March 2015 (SOL2015-03-11T16:22) are shown as a function of Doppler shift and time.

Profiles of Mg II lines, lines of C II and Si IV were obtained using the IRIS instrument before, during and after the X2.1 flare of 11 March 2015 (SOL2015- 03-11T16:22). We analyze the profiles of the five transitions of Mg II (the 3p − 3s h and k transitions, and three lines belonging to the 3d − 3p transitions). We use analytical methods to understand the unusual profiles, together with higher resolution observational data of similar phenomena observed by Jing and colleagues. The peculiar line ratios indicate anisotropic emission from the strands which have cross-strand line center optical depths (k-line) of between 1 and 10. The lines are broadened by unresolved Alfv ́enic motions whose energy exceeds the radiation losses in the Mg II lines by an order of magnitude. The decay of the line widths is accompanied by a decay in the brightness, suggesting a causal connection. If the plasma is

Graphic Caption: Intensity profiles of the Mg II h and k lines before during and after the X2.1 flare of 11 March 2015 (SOL2015-03-11T16:22) are shown as a function of Doppler shift and time.

Publication Name: ApJ

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