On the Nature of Off-limb Flare Continuum Sources Detected by SDO/HMI

0482570 - ASÚ 2018 RIV US eng J - Článek v odborném periodiku
Heinzel, Petr - Kleint, L. - Kašparová, Jana - Krucker, S.
On the Nature of Off-limb Flare Continuum Sources Detected by SDO/HMI.
Astrophysical Journal. Roč. 847, č. 1 (2017), 48/1-48/6. ISSN 0004-637X. E-ISSN 1538-4357
Grant CEP: GA ČR(CZ) GA16-18495S
Institucionální podpora: RVO:67985815
Klíčová slova: Sun * chromosphere * radiation mechanisms
Obor OECD: Astronomy (including astrophysics,space science)
Impakt faktor: 5.551, rok: 2017

In this paper we aim to determine which radiation mechanism is responsible for such enhancement being seen above the limb, at chromospheric heights around or below 1000 km. Using a simple analytical approach, we compare two candidate mechanisms, the hydrogen recombination continuum (Paschen) and the Thomson continuum due to scattering of disk radiation on flare electrons. Both mechanisms depend on the electron density, which is typically enhanced during the impulsive phase of a flare as the result of collisional ionization (both thermal and also non-thermal due to electron beams). We conclude that for electron densities higher than 10(12) cm(-3), the Paschen recombination continuum significantly dominates the Thomson scattering continuum and there is some contribution from the hydrogen free-free emission. This is further supported by detailed radiation-hydrodynamical (RHD) simulations of the flare chromosphere heated by the electron beams. We use the RHD code FLARIX to compute the temporal evolution of the flareheating in a semi-circular loop. The synthesized continuum structure above the limb resembles the off-limb flare structures detected by HMI, namely their height above the limb, as well as the radiation intensity. These results are consistent with recent findings related to hydrogen Balmer continuum enhancements, which were clearly detected in disk flares by the IRIS near-ultraviolet spectrometer.
Trvalý link: http://hdl.handle.net/11104/0277989