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Estimates of Densities and Filling Factors from a Cooling Time Analysis of Solar Microflares Observed with RHESSI  

Robert Baylor   Submitted: 2011-08-09 17:03

We use more than 4,500 microflares from the Reuven Ramaty High Energy SolarSpectroscopic Imager (RHESSI) microflare data set (Christe et al., 2008, Ap.J., 677, 1385) to estimate electron densities and volumetric filling factors ofmicroflare loops using a cooling time analysis. We show that if the fillingfactor is assumed to be unity, the calculated conductive cooling times are muchshorter than the observed flare decay times, which in turn are much shorterthan the calculated radiative cooling times. This is likely unphysical, but thecontradic- tion can be resolved by assuming the radiative and conductivecooling times are comparable, which is valid when the flare loop temperature isa maximum and when external heating can be ignored. We find that resultantradiative and con- ductive cooling times are comparable to observed decaytimes, which has been used as an assumption in some previous studies. Theinferred electron densities have a mean value of 1011.6 cm-3 and fillingfactors have a mean of 10-3.7. The filling factors are lower and densities arehigher than previous estimates for large flares, but are similar to those foundfor two microflares by Moore et al. (Ap. J., 526, 505, 1999).

Authors: R. N. Baylor, P. A. Cassak, S. Christe, I. G. Hannah, Säm Krucker, D. J. Mullan, M. A. Shay, H. S. Hudson, R. P. Lin
Projects: RHESSI

Publication Status: Published in Ap. J.
Last Modified: 2011-08-10 09:32
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Estimates of Densities and Filling Factors from a Cooling Time Analysis of Solar Microflares Observed with RHESSI

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