2024ApJ...966...86S

Using long-term X-ray observations, we present short-term and long-term X-ray variability analysis of the ultrafast rotating active star AB Dor. Flaring events are common in X-ray observations of AB Dor and occupy a substantial portion of the total observation time, averaging at around 57% ± 23%. The flare-free X-ray light curves show rotational modulation, indicating the presence of highly active regions in the star's corona. We have developed a light-curve inversion code to image the corona of active fast rotating stars. The results of coronal imaging reveal the presence of two active regions of different brightness that are separated by ∼180° in longitude. These active regions are also found to migrate along the longitude and also show variation in their brightness. Our analysis of long-term X-ray data spanning from 1979 to 2022 shows multiple periodicities. The existence of a ∼19.2 yr cycle and its first harmonic indicates the presence of a solar-like, long-term pattern. In comparison, the periodicities of ∼3.6 and ∼5.4 yr are possibly due to the presence of a flip-flop cycle in the X-rays, which is also supported by findings for similar periods from the optical data in earlier studies. Further confirmation of the existence of the X-ray flip-flop cycle requires long-term observations at regular intervals in the quiescent state.