Ryan O. Milligan, Phillip C. Chamberlin, Hugh S. Hudson, Thomas N. Woods, Mihalis Mathioudakis, Lyndsay Fletcher, Adam F. Kowalski, Francis P. Keenan
Observations of extreme-ultraviolet (EUV) emission from an X-class solar
flare that occurred on 2011 February 15 at 01:44 UT are presented, obtained
using the EUV Variability Experiment (EVE) onboard the Solar Dynamics
Observatory. The complete EVE spectral range covers the free-bound continua of
H I (Lyman continuum), He I, and He II, with recombination edges at 91.2, 50.4,
and 22.8 nm, respectively. By fitting the wavelength ranges blue-ward of each
recombination edge with an exponential function, lightcurves of each of the
integrated continua were generated over the course of the flare, as well as
emission from the free-free continuum (6.5-37 nm). The He II 30.4 nm and
Lyman-alpha 121.6 nm lines, and soft X-ray (0.1-0.8 nm) emission from GOES are
also included for comparison. Each free-bound continuum was found to have a
rapid rise phase at the flare onset similar to that seen in the 25-50 keV
lightcurves from RHESSI, suggesting that they were formed by recombination with
free electrons in the chromosphere. However, the free-free emission exhibited a
slower rise phase seen also in the soft X-ray emission from GOES, implying a
predominantly coronal origin. By integrating over the entire flare the total
energy emitted via each process was determined. We find that the flare energy
in the EVE spectral range amounts to at most a few per cent of the total flare
energy, but EVE gives us a first comprehensive look at these diagnostically
important continuum components.
View original:
http://arxiv.org/abs/1202.1731
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