Hot X-ray onsets of solar flares

Hudson H.S.; Simoes P.J.A.; Fletcher L.; Hayes L.A.; Hannah I.G.

Hot X-ray onsets of solar flares

Tipo

Artigo

Data de publicação

2021

Periódico

Monthly Notices of the Royal Astronomical Society

Citações (Scopus)

29

Autores

Hudson H.S.
Simoes P.J.A.
Fletcher L.
Hayes L.A.
Hannah I.G.

Resumo

© 2020 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.The study of the localized plasma conditions before the impulsive phase of a solar flare can help us understand the physical processes that occur leading up to the main flare energy release. Here, we present evidence of a hot X-ray 'onset' interval of enhanced isothermal plasma temperatures in the range of 10-15 MK over a period of time prior to the flare's impulsive phase. This 'hot onset' interval occurs during the initial soft X-ray increase and definitely before any detectable hard X-ray emission. The isothermal temperatures, estimated by the Geostationary Operational Environmental Satellite X-ray sensor, and confirmed with data from the Reuven Ramaty High Energy Solar Spectroscopic Imager, show no signs of gradual increase, and the 'hot onset' phenomenon occurs regardless of flare classification or configuration. In a small sample of four representative flare events, we tentatively identify this early hot onset soft X-ray emission to occur within footpoint and low-lying loop regions, rather than in coronal structures, based on images from the Atmospheric Imaging Assembly. We confirm this via limb occultation of a flaring region. These hot X-ray onsets appear before there is evidence of collisional heating by non-thermal electrons, and hence challenge the standard modelling techniques.

Assuntos Scopus

Corona , Energy release , Flare , Impulsive phase , Localised , Physical process , Plasma conditions , Soft X-ray , Solar flare , X-ray emission