The 2014 March 29 X-flare: Subarcsecond Resolution Observations of Fe XXI λ1354.1
Abstract
The Interface Region Imaging Spectrometer (IRIS) is the first solar instrument to observe ~10 MK plasma at subarcsecond spatial resolution through imaging spectroscopy of the Fe XXI λ1354.1 forbidden line. IRIS observations of the X1 class flare that occurred on 2014 March 29 at 17:48 UT reveal Fe XXI emission from both the flare ribbons and the post-flare loop arcade. Fe XXI appears at all of the chromospheric ribbon sites, although typically with a delay of one raster (75 s) and sometimes offset by up to 1''. 100-200 km s-1 blue-shifts are found at the brightest ribbons, suggesting hot plasma upflow into the corona. The Fe XXI ribbon emission is compact with a spatial extent of <2'', and can extend beyond the chromospheric ribbon locations. Examples are found of both decreasing and increasing blue-shift in the direction away from the ribbon locations, and blue-shifts were present for at least six minutes after the flare peak. The post-flare loop arcade, seen in Atmospheric Imaging Assembly 131 Å filtergram images that are dominated by Fe XXI, exhibited bright loop-tops with an asymmetric intensity distribution. The sizes of the loop-tops are resolved by IRIS at >=1'', and line widths in the loop-tops are not broader than in the loop-legs suggesting the loop-tops are not sites of enhanced turbulence. Line-of-sight speeds in the loop arcade are typically <10 km s-1, and mean non-thermal motions fall from 43 km s-1 at the flare peak to 26 km s-1 six minutes later. If the average velocity in the loop arcade is assumed to be at rest, then it implies a new reference wavelength for the Fe XXI line of 1354.106 ± 0.023 Å.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2015
- DOI:
- 10.1088/0004-637X/799/2/218
- arXiv:
- arXiv:1409.8603
- Bibcode:
- 2015ApJ...799..218Y
- Keywords:
-
- Sun: activity;
- Sun: chromosphere;
- Sun: corona;
- Sun: flares;
- Sun: UV radiation;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 30 pages, 13 figures, accepted by ApJ