What:	Electron Acceleration in Solar Flares
Who:	Dr. Siming Liu (刘四明）
	(University of Glasgow，UK)
When:	Tuesday afternoon, July 13th, 2:30 p.m
Where:	Room 516, Office Block, 2 West Beijing Road (PMO, CAS)
	Welcome to attend
	( PMO Academic committee & academic circulating committee)

　 abstract　

　 Plasma heating and particle acceleration are essential elements of solar flare study. To probe the underlying physical processes, we study flares associated with well-defined loop structures and with the impulsive hard X-ray (HXR) emission dominated by a single pulse, which significantly reduces the complexity of flare study introduced by the magnetic field configuration. With imaging spectroscopic observations of RHESSI, we find that for some flares, the X-ray spectrum can be fitted with an isothermal model. The impulsive HXR emission therefore can be attributed to a hot plasma in the coronal loop with the temperature and emission measure varying on a timescale of a few seconds. For most flare loops, the early impulsive phase spectra can still be fitted with an isothermal model. A high-energy power-law component, however, is needed to fit the spectra near the HXR peak. And the normalization and spectral index of this power-law component vary on a timescale comparable to the temperature and emission measure of the thermal component, suggesting that the X-ray emission is dominated by a single electron population. We also study a few flares with slightly more complex HXR light curves. The results suggest that the particle acceleration is highly intermittent and may not be well correlated with the evolution of the thermal component.