Simultaneous Optical and ROSAT Soft X-Ray Observations of Impulsive Bursts on the Flare Star UV Ceti

Abstract

Two small flares on the nearby flare star UV Ceti were simultaneously observed with ground-based, highspeed optical multicolor photometry and in soft X-rays using the ROSAT Observatory. Optically, each flare showed a brief (∼12 s duration) impulsive event. The second flare also showed a gradual phase lasting about 5 minutes. Upon closely examining the soft X-ray timing data, it was found that for both flares a soft X-ray burst followed the optical spike by about 30 s. The gradual phase of the second flare was accompanied by a rising and falling X-ray flux, as has been observed in numerous previous flares, but our timing data appear to show soft X-ray bursts continuing during this phase as well. These impulsive X-ray bursts may be the low energy tails of hard X-ray emission from particle beams