We found systematic microwave source motions along a flare-arcade using Nobeyama Radioheliograph (NoRH) 17 GHz images. The motions were associated with a X-class disk flare which occurred on 15th February 2011. 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 Radiopolarimeters (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 with several facts: 1) The microwave source moved systematically along the flare-arcade, which was observed by the AIA 94 A 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 for the first episode and 22 km/s for the second episode. The spectral slope of 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 the 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 A and 94 A 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.
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