The solar flare soft X-ray differential emission measure and the Neupert effect at different temperatures

Data from the Yohkoh Soft X-ray Telescope (SXT) and Bragg Crystal Spectrome ter (BCS) are used to obtain the differential emission measure (DEM) of sol ar flare soft X-ray plasma. The maximum entropy method is used to obtain th e DEM for 80 flares observed by SXT and BCS from 1991 October to 1992 Novem ber. We find that it is often difficult to describe the DEM using a monoton ically decreasing function; functions with a hump at high temperature are o ccasionally more useful. From the time history of the DEM, we show that hig her temperature plasma peaks earlier and cools faster. We also show that hi gh-temperature plasma (>16.5 MK) is more likely than low-temperature plasma to exhibit the so-called Neupert effect, in which the time derivative of t he soft X-ray emission measure is similar to the light curve of the impulsi ve hard X-ray emission for the flare.