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26 April 2024 |
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Article overview
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Super-hot (T > 30 MK) Thermal Plasma in Solar Flares | | Amir Caspi
; | | Date: |
10 May 2011 | | Abstract: | The Sun offers a convenient nearby laboratory to study the physical processes
of particle acceleration and impulsive energy release in magnetized plasmas
that occur throughout the universe, from planetary magnetospheres to black hole
accretion disks. Solar flares are the most powerful explosions in the solar
system, releasing up to 10^32-10^33 ergs over only 100-1,000 seconds,
accelerating electrons up to hundreds of MeV and heating plasma to tens of MK.
The accelerated electrons and the hot plasma each contain tens of percent of
the total flare energy, indicating an intimate link between particle
acceleration, plasma heating, and flare energy release. The Reuven Ramaty High
Energy Solar Spectroscopic Imager (RHESSI) observes the X-ray emission from
these processes from ~3 keV to ~17 MeV with unprecedented spectral, spatial,
and temporal resolution. RHESSI observations show that "super-hot" (>30 MK)
plasma temperatures are achieved almost exclusively by intense, GOES X-class
flares and appear to be strictly associated with coronal magnetic field
strengths exceeding ~170 Gauss, suggesting a direct link between the magnetic
field and heating of super-hot plasma. Images and spectra of the 2002 July 23
X4.8 event reveal that the super-hot plasma is both spectrally and spatially
distinct from the commonly-observed ~10-20 MK plasma, and is located above the
cooler source. It exists with high density even during the pre-impulsive phase,
which is dominated by coronal non-thermal emission with negligible footpoints,
suggesting that, rather than the traditional picture of chromospheric
evaporation, the origins of super-hot plasma may be the compression and
subsequent thermalization of ambient material accelerated in the reconnection
region above the flare loop, a physically-plausible process not detectable with
current instruments but potentially observable with future telescopes. | | Source: | arXiv, 1105.1889 | | Services: | Forum | Review | PDF | Favorites | |
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