Chromospheric density and height measurements of the 2002-Feb-20 flare observed with RHESSI

Details Chromospheric density and height measurements of the 2002-Feb-20 flare observed with RHESSI Chromospheric density and height measurements of the 2002-Feb-20 flare observed with RHESSI

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002esasp.506..275a&link_type=abstract

In: Solar variability: from core to outer frontiers. The 10th European Solar Physics Meeting, 9 - 14 September 2002, Prague, Cze

Physics

1

Sun: Corona, Sun: Chromosphere, Hard X-Rays, Rhessi Observations

Scientific paper

We present the first chromospheric density and height measurements made with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft during the flare of 2002-Feb-22, 11:06 UT. Thanks to the high energy resolution of the germanium-cooled hard X-ray detectors on RHESSI we can measure the flare source positions with a high accuracy as a function of energy. Using a forward-fitting algorithm for image reconstruction, we find a systematic decrease in the altitudes of the source centroids z(ɛ) as a function of increasing hard X-ray energy ɛ, as expected in the thick-target bremsstrahlung model of Brown. The altitude of hard X-ray emission as a function of photon energy ɛ can be characterized by a powerlaw function in the ɛ = 15-50 keV energy range, viz. z(ɛ) ≍ 2.3 (ɛ/20 keV)-1.3 Mm. Based on a purely collisional 1-D thick-target model, this height dependence can be inverted into a chromospheric density model n(z), which follows the powerlaw function ne(z) = 1.25×1013 (z/1 Mm)-2.5 cm-3. This density is comparable with models based on optical/UV spectrometry in the chromospheric height range, while at a height of h≍1000-2500 km, it is more consistent with the "spicular extended-chromosphere model" inferred from radio sub-mm observations. In coronal heights of the flare loop, the RHESSI inferred desities are comparable with soft X-ray and radio observations.

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