VLA observations of postflare loops at 20 centimeter wavelength

Abstract

From observations with the VLA on May 19, 1979, the first spatially resolved observations of 20 cm radio emission originating from postflare loop systems are presented. The 20 cm burst was associated with an H alpha flare and a soft X-ray burst, and most of the intense radio emission occurred at the end of the H alpha flare and in the decay phase of the X-ray burst. The 20 cm 'snapshot' maps of the burst source obtained with a resolution of 12 arcsec x 24 arcsec show that the radio emission occurred in structures that are similar in size and shape to the systems of loops observed in X-rays. This postflare radio emission is considered to be similar to the H alpha and X-ray emissions originating in postflare loops. The radio observations of postflare loops have the unique advantage that they offer an important means of determining the average magnetic field strength in these loops. Interpreting the radio emission in this particular event as thermal gyroradiation or as nonthermal synchrotron radiation, the magnetic field strength is estimated to lie in the range of approximately 120-170 gauss.