RHESSI, TRACE, and the Spatial Neupert Effect

We combine RHESSI and TRACE observations to investigate the spatial and temporal associations between hard X-ray (HXR) and extreme ultraviolet (EUV) emissions in impulsive bursts observed during the GOES X flare of April 21, 2002. The RHESSI HXR (above 25 keV) time profile for this event is in general agreement with the time derivative of the GOES soft X-ray (1 to 8-A) flux. This temporal correlation - the Neupert Effect - is consistent with nonthermal thick-target electrons being the primary source of heating of the soft X-ray emitting thermal plasma during the flare impulsive phase.

To further investigate the link between nonthermal electrons and thermal soft X-ray emission, we examine the spatial and temporal behavior of HXR emission in high-resolution (2-3 arcsecs) RHESSI images. Specifically, we identify regions of enhanced HXR emission and compare their lightcurves with corresponding lightcurves observed simultaneously with the TRACE 195-A filter at 1-arcsec spatial resolution. The TRACE 195-A bandpass contains contributions from Fe XII and Fe XXIV lines which are sensitive to plasmas at temperatures of near 1.5 MK and 15-20 MK, respectively. Consequently, when used in conjunction with GOES, the TRACE 195-A flux provides a useful proxy for investigating the spatial properties of flare-heated thermal plasma.