Very large array observations of coronal loops at 20 centimeter wavelength

Looplike coronal structures have been observed in VLA synthesis maps at 20 cm wavelength with an angular resolution of 3.''7 x 5''. The 20 cm loops extend across regions of opposite magnetic polarity in the underlying photosphere. The absence of detectable circular polarization suggests that the 20 cm loops are optically thick with brightness temperatures equal to coronal electron temperatures of millions of degrees. We interpret the 20 cm emission in terms of the optically thick bremsstrahlung of thermal electrons trapped within magnetic loops which are in hydrostatic equilibrium. The 20 cm loops have temperature maxima in their central regions as is expected from hydrostatic loops, and they also satisfy the hydrostatic scaling relation. The semilength Lroughly-equal5 x 109 cm, maximum electron temperature T/sub e/(max)roughly-equal3 x 106 K, pressure p = 2 dyn cm-2, and electron density N/sub e/roughly-equal2.5 x 109 cm-3 of the 20 cm loops are all characteristic of the coronal loops detected at X-ray wavelengths. This discovery opens up the possibility of using 20 cm synthesis maps to investigate the detailed structure, evolution, and preflare activity of coronal loops