Late-phase hard X-ray emission from flares

In a few major flare events observed by RHESSI, we see hard X-ray signatures long after (tens of minutes to more than one hour) the impulsive-phase onset. A prototype for such phenomena was the flare of March 31, 1969 (Frost and Dennis, 1971). Recent RHESSI examples include January 19, 2005, a GOES X1.5 event with gradual variations, and September 7, 2005 an X17 event with more impulsive variability. RHESSI images show footpoint emissions in both cases; the spectra are hard and become harder with time as in the Frost-Dennis event. The existence of impulsive variability and footpoint emission allows us to discuss trapping and injection. We discuss the morphology of these events, including other examples such as April 21, 2002 (X1.5).