High-density Off-limb Flare Loops Observed by SDO

0497539 - ASÚ 2019 RIV US eng J - Journal Article
Jejčič, Sonja - Kleint, L. - Heinzel, Petr
High-density Off-limb Flare Loops Observed by SDO.
Astrophysical Journal. Roč. 867, č. 2 (2018), č. článku 134. ISSN 0004-637X. E-ISSN 1538-4357
R&D Projects: GA ČR(CZ) GA16-18495S; GA ČR(CZ) GA16-16861S
Institutional support: RVO:67985815
Keywords : Sun * flares * radio radiation
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 5.580, year: 2018
Method of publishing: Open access

On 2017 September 10, a prominent loop system appeared during the gradual phase of an X8.2 flare (SOL2017-09-10), visible in all passbands of SDO/AIA and in the white-light continuum of SDO/HMI. We investigate its electron density by taking into account all radiation processes in the flare loops, i.e., the Thomson continuum, hydrogen Paschen and Brackett recombination continua, as well as free–free continuum emission. We derive a quadratic function of the electron density for a given temperature and effective loop thickness. By absolutely calibrating SDO/HMI intensities, we convert the measured intensities into electron density at each pixel in the loops. For a grid of plausible temperatures between cool (6000 K) and hot (106 K) structures, the electron density is computed for representative effective thicknesses between 200 and 20,000 km. We obtain a relatively high maximum electron density, about 1013 cm‑3. At such high electron densities, the Thomson continuum is negligible and therefore one would not expect a significant polarization degree in dense loops. We conclude that the Paschen and Brackett recombination continua are dominant in cool flare loops, while the free–free continuum emission is dominant for warmer and hot loops.
Permanent Link: http://hdl.handle.net/11104/0290095