A TEST OF A NEW FLARE LOOP SCALING LAW USING YOHKOH SXT AND GOES OBSERVATIONS

We compare the lengths of coronal loops observed on the Sun using the Soft X-Ray Telescope on Yohkoh with those predicted from the theoretic al model of Hawley et al. This model relates the temporal behavior of coronal emission observed during flares on active stars to the length of the loops undergoing flaring. In that model, the footpoint-to-footp oint loop length 2L (measured in kilometers) should obey the relations hip 2L similar or equal to 0.01Y, where Y = 1.26 tau(r)(3/7)tau(d)(4/7 )T(A)(1/2), is the ''rise time'' (in seconds) from flare onset to flar e peak, tau(d) is the ''decay time'' (s) from flare peak to the time w hen the emission measure is 25% of its peak value, and T-A (K) is the temperature at the top of the loop at flare peak. The observations sho w a strong correlation between 2L and Y, with the theoretical relation ship consistent with observed loop lengths in most cases. For a few lo ops, the theoretical model tends to somewhat overpredict the loop leng th. When the observed loop lengths are fitted to a single power-law re lationship in Y, we find the data are best fitted by log 2L = log (0.4 4 +/- 0.05) + (0.75 +/- 0.05) log Y. We offer no quantitative theoreti cal justification for this relationship, but we do suggest several rea sons why the Hawley et at model overpredicts loop lengths in some case s.