Photospheric magnetic activities responsible for soft X-ray pointlike microflares. I. Identifications of associated photospheric/chromospheric activities

By combining Yohkoh soft X-ray images with high-resolution magnetograms simultaneously obtained at La Palma, we studied photospheric magnetic signatures responsible for soft X-ray microflares (active-region transient brightenings). In order to have a reliable correspondence between the photosphere and the corona, we studied 16 pointlike transient brightenings with X-ray source size less than 10 occurring during periods when the seeing was excellent at La Palma, although a lot of transient brightenings were in forms of multipleor single-loop structures. In half of the studied events, small-scale emergences of magnetic flux loops are found in the vicinity of the transient brightenings. Six events of that half show that a small-scale flux emergence accompanies the X-ray brightening 5-30 minutes prior to its onset. In the other half of the studied events, no apparent evolutionary change of magnetic flux elements is found associated with the transient brightenings. Many of these events are found in rather strong magnetic fields, such as sunspots and pores, implying that small-scale changes of magnetic flux are obscured or suppressed by strong magnetic fields. The horizontal plasma flows derived from local cross-correlation tracking of granules in continuum images are suppressed at the feet of some X-ray transient brightenings.