Physics
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsp52a..05d&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #SP52A-05
Physics
7519 Flares, 7554 X Rays, Gamma Rays, And Neutrinos
Scientific paper
We investigate the initial stage of chromospheric evaporation in flares using soft X-ray flare spectra obtained by the Bragg Crystal Spectrometer (BCS) experiment on Yohkoh. We determine the minimum detectable soft X-ray flare volume emission measure from BCS Ca XIX flare spectra. We find that the minimum detectable emission measure by BCS is produced by an X-ray flux that is about equal to the peak intensity of a class A5 flare. We also find that the centroid wavelength of the Ca XIX line in spectra with the first detectable emission is within about 8.5E-4 Angstroms of the rest wavelength, which is 80 km/s in terms of a Doppler shift. We interpret our results assuming sequential chromospheric evaporation into a multi-threaded flare loop envelop. Under this assumption, by comparing the BCS results with images of flares from the Soft X-ray Telescope (SXT) on Yohkoh and from TRACE, we have determined the minimum energy and electron density of multi-million degree soft X-ray plasma that can be detected using presently available spectroscopic X-ray data. In addition we consider the implications of a multi-thread loop model on TRACE and Yohkoh flare images, and the differences between the images and the multi-thread predictions. We find that the multi-million degree flare plasma in TRACE images frequently exhibits structures that do not resemble the images of loops expected from the numerical simulations of evaporation. Thus, while observational signatures of flare dynamics can be consistent with chromospheric evaporation simulations, problems still remain in understanding the loop morphology of the multi-million degree plasma.
Doschek George A.
Warren Harry P.
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