Explosive events and transition region blinkers: Time variability of non-Gaussian quiet Sun EUV spectra

The transition region (TR) from the chromosphere to the corona of the Sun and solar type stars is a very dynamic regime. On the Sun at least two major observational classes of transients can be seen: explosive events and blinkers. Besides these transients there is also a more steady spectral component in transition region lines that accounts for the deviation of the line profile from a (single) Gaussian shape, i.e. for enhanced wings that are well described by a second broad Gaussian, a tail component. The present paper discusses the spectral properties of these features in order to learn more about a possible connection between blinkers, explosive events and tail components. This paper will show that explosive events are most probably not related to the tail components or to transition region blinkers. During a blinker not only the intensity rises, as described by many CDS studies, but also the line width and shift are changing, as we show with SUMER spectra. The variation in line shift and width is closely related to the intensity variation. The line width drops to very small values at the midst of a blinker, almost reaching the thermal line width, while at the same time the Doppler shifts reach a maximum value. From this we may conclude that blinkers are driven by events in the chromosphere heating a loop asymmetrically and powering a strong laminar flow through the loop.