CORONAL DYNAMICS OF A QUIESCENT ACTIVE REGION

Shortly after the repair of the Solar Maximum Mission, an observation was made with the Flat Crystal Spectrometer (FCS) to investigate coronal X-ray line broadening in a nonflaring active region. The resulting map of FCS line profiles across the central X-ray bright portion of a large active region shows a clear variation in line width for the Mg XI resonance line at 9.17 angstrom, but no evidence of line shifts. Line ratios yield electron temperatures T(e) approximately 3 x 10(6) K within 10% for most of the map. The line widths range from narrow (i.e., consistent with thermal Doppler broadening) to broad (where the width in excess of the thermal Doppler value is greater than the thermal width). The brightest, broadest profiles are consistent with emission from the tops of loops overlying the magnetic neutral line. For the spatially averaged Mg XI resonance line profile, the "excess velocity," upsilon-ex, corresponding to the excess width above the thermal value is equal to the thermal velocity for Mg ions, 45 km s-1; for some individual bright pixels, upsilon-ex greater-than-or-equal-to 60 km s-1 with high significance (greater-than-or-equal-to 5-sigma). An instrumental source for the broadening is ruled out by the presence of narrow (i.e., only thermally broadened) line profiles in some areas of the map; contributions from higher temperature plasma are inconsistent with the observed lack of flux in the high-temperature FCS channels. We interpret the observed coronal line broadening as a signature of the mechanism(s) responsible for coronal heating in active regions.