A systematic study of non-thermal emissions to search for characteristics of white-light flares and comparison with magnetic features

It is believed that the origin of white-light enhancement is accelerated non-thermal electrons. The difference of the relationship between emission measure and temperature of white-light flares (WLFs) and no white-light flares (NWLFs) supported the existence of strong magnetic field around the acceleration site (Watanabe et al., 2017). Although the field strength at the acceleration site cannot measure directly, it can be estimated by using the turn-over frequency of gyro-synchrotron emission in microwaves (Dulk 1985). Then we performed a systematic study of microwave turn-over frequencies observed with the Nobeyama Radio polarimeters (NoRP) for >M3 class flares during the period from January 2011 to December 2017. We found 51 events which were simultaneously observed with white-light (Hinode/SOT and/or SDO/HMI) and microwave (NoRP), however, we couldn't find any difference in turn-over frequencies for WLF and NWLF. Then, we determined emission locations of hard X-ray (HXR) and microwave observed by the RHESSI and Nobeyama Radioheliograph (NoRH) respectively, we only choose the events which have loop-top microwave source and compare turn-over frequencies for WLF and NWLF. However, this study didn’t show any difference in the turn-over frequencies for WLF and NWLF. This is because the turn-over frequency is determined by not only the field strength but also the electron density (Dulk 1985), we have to think about the variation of electron density for this study. We also determined field strength and temperature of white-light emission site by using SDO/HMI and the three continuum bands of Hinode/SOT respectively, and searched for some correlation with white-light emission strength. Although we couldn't find any correlation between them, we want to discuss magnetic field structure of WLFs.