Long-lived microwave pulsations observed in a complex solar active region

Abstract

Microwave pulsations were detected on Sept. 13, 1977 in the intense emission from a compact microwave source associated with the large, slowly rotating, and magnetically complex solar active region, McMath 14943. These pulsations persisted over 5-1/2 hours, with the dominant repetition rate remaining close to 0.4 Hz; they were not associated with flare activity. The core of the microwave emission was located over a plage rather than over the major spot in the region. A mechanism for the pulsating source is proposed in which radial oscillations in an arched magnetic flux tube modulate the gyrosynchrotron emission from high energy electrons trapped in the tube.