First Observation of the Full Hard X-ray Spectral Signature of Nonuniform Ionization and Derivation of the Density Distribution in the Flaring Loop

Details First Observation of the Full Hard X-ray Spectral Signature of Nonuniform Ionization and Derivation of the Density Distribution in the Flaring Loop First Observation of the Full Hard X-ray Spectral Signature of Nonuniform Ionization and Derivation of the Density Distribution in the Flaring Loop

May 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21640419s&link_type=abstract

American Astronomical Society, AAS Meeting #216, #404.19; Bulletin of the American Astronomical Society, Vol. 41, p.903

Astronomy and Astrophysics

Astronomy

Scientific paper

Compared with the simple collisional thick-target model, the nonuniform ionization thick-target model includes a region below the fully ionized corona where the plasma is fully un-ionized. The X-ray emission from this region is enhanced by a factor of up to 2.8. As a result, the X-ray spectrum from a nonuniform ionization target (assuming that the electron distribution is single-power-law) has both break-up and break-down features. However, due to the presence of thermal emission, the break-up feature usually cannot be observed.
We report the first observation of the full spectrum expected from nonuniform ionization in the thick-target region. The flare, a GOES X1.2 class flare, peaked at 16:51:08 on 31 Oct. 2002 in hard X-ray. The RHESSI X-ray spectral analysis shows both the break-up and break-down features at this peak time and a break energy of over 100 keV at the peak. The time evolution of the break energy is derived. The results indicate that the ionized plasma erupted into the loop and continued to fill the loop after the hard X-ray peak.
We also present a method to obtain the plasma density in the flaring loop from hard X-ray images. The ratio of the HXR flux above and below a given depth can be used to determine the column density at that depth, and therefore the average density above that depth. We can determine the density-depth distribution during flare using this method. The densities we got at the peak time are 1.1×1011, 3.5×1011 and 1.7×1012 cm-3 at the depth of 4.7, 7.1 and 8.5 Mm below the top of the loop (or column density of 5.3×1019, 1.4×1020 and 3.8×1020 cm-2), respectively.

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