Plasma and Magnetic Field Properties of Coronal Loops Observed at High Spatial Resolution

摘要

Compared are coordinated, high spatial resolution observations in soft X-rays-in microwaves at 1.45 GHz (20 cm) and 4.9 GHz (6 cm) and with photospheric magnetograms, of six coronal loops. The loops were found to have plasma parameters typical of quiescent active region loops. Each loop had a compact microwave source with T sub b = 1-2.5 million K cospatial with or near the loop apex. Contrary to some interpretations, no complete loops (as determined by the X-ray observations) were imaged in microwaves. Model loops using the derived observational plasma and magnetic parameters are constructed, and the predicted distribution of thermal microwave emission compared with observations. The loop emission observed at 4.9 GHz is best described by fourth harmonic gyroresonance emission from a dipole loop model, but with less field variation along the loop than in another model. The 1.45 GHz emission is likely to be free-free, since the X-ray loops are optically thick to free-free emission. The modeling results require the existence of an external plasma around the X-ray loops with a temperature of about 100,000 K or less. One can also deduce or place constraints on the magnetic field strengths within and their variations along the loops.