Hot X-ray Onsets of Solar Flares. (arXiv:2007.05310v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hudson_H/0/1/0/all/0/1">Hugh S. Hudson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Simoes_P/0/1/0/all/0/1">Paulo J. A. Simoes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fletcher_L/0/1/0/all/0/1">Lyndsay Fletcher</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hayes_L/0/1/0/all/0/1">Laura A. Hayes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hannah_I/0/1/0/all/0/1">Iain G. Hannah</a>
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 up to tens of seconds prior to the flare’s impulsive phase. This `hot
onset’ interval occurs during the initial soft X-ray increase and prior to the
detectable hard X-ray emission. The isothermal temperatures, estimated by the
Geostationary Operational Environmental Satellite (GOES) X-ray sensor, and
confirmed with data from the Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI), 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 identify this early hot
onset soft X-ray emission mainly within footpoint and low-lying loops, rather
than with coronal structures, based on images from the Atmospheric Imaging
Assembly (AIA). 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 they challenge the standard flare heating
modeling techniques.
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 up to tens of seconds prior to the flare’s impulsive phase. This `hot
onset’ interval occurs during the initial soft X-ray increase and prior to the
detectable hard X-ray emission. The isothermal temperatures, estimated by the
Geostationary Operational Environmental Satellite (GOES) X-ray sensor, and
confirmed with data from the Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI), 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 identify this early hot
onset soft X-ray emission mainly within footpoint and low-lying loops, rather
than with coronal structures, based on images from the Atmospheric Imaging
Assembly (AIA). 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 they challenge the standard flare heating
modeling techniques.
http://arxiv.org/icons/sfx.gif
