HARD X-RAY-EMISSION FROM ACTIVE-REGION TRANSIENT BRIGHTENINGS

We present the results of a search for hard X-ray counterparts to soft X-ray transient brightenings in solar Active Region 7260 based on dat a from the soft and hard X-ray telescopes on board the Yohkoh spacecra ft. A total of 72 soft X-ray events are found to accompany hard X-ray emission. They represent strong transient brightenings. The scatter pl ot between the time-integrated hard X-ray flux and the peak soft X-ray flux indicates that these transient brightenings are not particularly hard X-ray-rich or -deficient in comparison with more intense flares. As in flares, hard X-ray emission is most noticeable during the rise phase of the soft X-ray temporal variations, indicative of its nonther mal origin. We conclude that these soft X-ray transient brightenings a re nothing but small flares and predict that hard X-ray emission could be detected from less intense events if an instrument with higher sen sitivity were available.