[PEM12-P05] Energy Budget in Cold Solar Flares Observed with Nobeyama Radioheliograph
Keywords:Solar flare, radio, particle acceleration
A hint to solve this problem could be provided by some extreme flares such as thermal-rich flares and purely nonthermal flares. In this study, we focused on so-called cold flare which shows significant nonthermal emissions with relatively very small amount of thermal emissions. We have already analyzed a cold solar flare occurring on 10 March 2011. This flare was well observed with Nobeyama Radioheliograph (NoRH). It shows a significant microwave enhancement (about 210 SFU at 17GHz). This microwave enhancement is produced via gyro-synchrotron emissions by high-energy electrons. However, any significant enhance was not found in the GOES X-ray light curve during the flare period. RHESSI did not observe this flare, but Suzaku detected hard X-rays in the energy range above 100 keV. So it was confirmed that electrons were actually accelerated while plasma heating process did not work well in this flare. The characteristics of this flare were short duration and very compact size. From these facts, we concluded that the magnetic field of the loop top region might be very intense. This might be a key how a cold flare is produced. To confirm this, we need more analyses of similar events. From the event list of NoRH, we pick up candidates of cold flares which show a significant microwave enhancement without any counterpart in soft X-rays and analyze them. The characteristics seem to be the same as the previous event. Then we discuss why thermal emissions (plasma heating) are suppressed in these flares.