The Effect of Radiative Cooling on Coronal Loop Oscillations

Abstract

Coronal loops that exhibit kink-mode oscillations have generally been assumed to have a constant density and temperature during the observed time interval. Analyzing their intensities in an EUV wave band, however, clearly shows that their brightness varies in a way that is consistent with a temperature cooling through the EUV passband, which limits their detection time, observed damping time, and number of observable periods. We study kink-mode oscillations of eight loops observed during the so-called harmonica event on 2001 April 15, 21:58–22:27 UT in the 171 band. We find loop densities of cm Ϫ3 , loop widths of Mm, and A n p (1.4 ‫ע‬ 0.6) # 10 w p 2.0 ‫ע‬ 2.6 e e-folding cooling times of minutes, when they cool through the peak temperature MK of t p 17 ‫ע‬ 7 T p 0.95 cool the 171 band. We conclude that oscillations of a single loop cannot be detected longer than 10–20 minutes i A one single filter and appropriate light curve modeling is necessary to disentangle the subsequent oscillation phases of multiple near-cospatial loops.