Systematic Microwave Source Motions along a Flare-Arcade Observed by Nobeyama Radioheliograph and AIA/SDO

We found systematic microwave source motions along a flare-arcade using Nobeyama Radioheliograph (NoRH) 17 GHz images. The motions were associated with an X-class disk flare that occurred on 2011 February 15. For this study, we also used EUV images from Atmospheric Imaging Assembly (AIA) and magnetograms from Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory, and multi-channel microwave data from Nobeyama Radio Polarimeters (NoRP) and Korean Solar Radio Burst Locator (KSRBL). We traced centroids of the microwave source observed by NoRH 17 GHz during the flare, and found two episodes of the motion based on several facts: (1) The microwave source moved systematically along the flare-arcade, which was observed by the AIA 94 angstrom channel, in a direction parallel to the neutral line. (2) The period of each episode was 5 min and 14 min, respectively. (3) Estimated parallel speed was 34 km s(-1) for the first episode and 22 km s(-1) for the second episode. The spectral slope of the microwave flux above 10 GHz obtained by NoRP and KSRBL was negative for both episodes, and for the last phase of the second episodes it was flat with a flux of 150 sfu. The negative spectrum and the flat with high flux indicate that the gyrosynchrotron emission from accelerated electrons was dominant during the source motions. The sequential images from the AIA 304 angstrom and 94 angstrom channels revealed that there were successive plasma eruptions, and each eruption was initiated just before the start time of the microwave sources motion. Based on the results, we suggest that the microwave source motion manifests the displacement of the particle acceleration site caused by plasma eruptions.