SLOW-MODE OSCILLATIONS OF LARGE-SCALE CORONAL LOOPS

On several occasions, repetitive X-ray brightenings, sometimes accompa nied by mass injections into adjacent loops, appeared quasi-periodical ly with mean periods dose to 20 minutes. In all cases when X-ray image s were available, the sites of these brightenings were in active regio ns which were associated with large-scale coronal loops of length (2 - 3) x 10(5) km. Therefore, the primary source of these long-periodic p ulsations might be slow-mode oscillations in these large-scale loops. Free MHD oscillations, proposed earlier by Roberts, Edwin, and Benz (1 984), may fit the observed data.