A brightening coronal loop observed by TRACE. II. Loop modeling and constraints on heating

This is the second of two papers dedicated to the brightening of a coronal loop observed by the Transition Region and Coronal Explorer (TRACE) on 1998 June 26; it aims at hydrodynamic modeling of the brightening. Since the lo op geometry is practically unchanged during the brightening, the evolution of the plasma cofined in the loop is described with a one-dimensional hydro dynamic time-dependent numerical model, and from the results the emission a long the loop in the TRACE 171 Angstrom band is synthesized. The informatio n from Paper I is used to derive the geometry and the initial configuration of the loop as well as for comparison with the results of the model. The m odeling is focused to determine the amount, spatial distribution, and evolu tion of the heating deposited in the loop to make the modeled evolution clo se to that observed with TRACE. We find that, in order to match the observe d evolution and distribution of the brightness along the loop, the heating has to be nonsymmetrical in the loop, in particular, deposited between the apex and one footpoint (3 x 10(9) cm from the southern footpoint). A reason able match with observations is obtained by assuming that the heating is sw itched on abruptly and then kept constant for the whole rising phase. An ev en better match is obtained with the heating high and constant for 100 s an d then decaying exponentially with an e-folding time of 300 s. We discuss t he resulting physical scenario; a bright irregular structure close to the l oop in the TRACE images may be a tracer of the heating release.