Transition region bright dots in active regions observed by the Interface Region Imaging Spectrograph

Abstract

The Interface Region Imaging Spectrograph (IRIS) reveals numerous small-scale (sub-arcsecond) brightenings that appear as bright dots sparkling the solar transition region in active regions. Here, we report a statistical study on these transition region bright dots. We use an automatic approach to identify 2742 dots in a Si IV raster image. We find that the average spatial size of the dots is 0.8 arcsec$^2$ and most of them are located in the faculae area. Their Doppler velocities obtained from the Si IV 1394 {\AA} line range from -20 to 20 km/s. Among these 2742 dots, 1224 are predominantly blue-shifted and 1518 are red-shifted. Their nonthermal velocities range from 4 to 50 km/s with an average of 24 km/s. We speculate that the bright dots studied here are small-scale impulsive energetic events that can heat the active region corona.