Abstract:
We present the analyses of intense X-ray flares detected on the active fast rotator AB Dor using observations from the XMM–
Newton. A total of 21 flares are detected, and 13 flares are analysed in detail. The total X-ray energy of these flares is found to be
in the range of 1034−36 erg, in which the peak flare flux increased up to 34 times from the pre-/post-flaring states for the strongest
observed flare. The duration of these flaring events is found to be 0.7 to 5.8 h. The quiescent state X-ray spectra are found to be
explained by a three-temperature plasma with average temperatures of 0.29, 0.95, and 1.9 keV, respectively. The temperatures,
emission measures, and abundances are found to be varying during the flares. The peak flare temperature was found in the
31–89 MK range, whereas the peak emission measure was 1052.5–54.7 cm−3 . The abundances vary during the flares and increase
by a factor of ∼3 from the quiescent value for the strongest detected flare. The variation in individual abundances follows the
inverse-FIP effect in quiescent and flare phases. The X-ray light curves of AB Dor are found to exhibit rotational modulation.
The semi-loop lengths of the flaring events are derived in the range of 109.9−10.7 cm, whereas the minimum magnetic field to
confine the plasma in the flaring loop is estimated between 200 and 700 G.
