Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades

Abstract

Together with coronal mass ejection, flares are the most energetic stellar magnetic events, ignited by a sudden release of magnetic energy, which triggers a cascade of interconnected phenomena, each resulting in emission in different bands. For this reason, flares are intrinsic multiwavelength phenomena. In particular, optical and soft X‐ray emission probes two different events occurring during flares: the heating of plasma in the upper photosphere at the footpoints of the magnetic loops and the heating and cooling of the plasma confined in the loops in the corona, respectively. To characterize powerful flares observed in optical and X‐rays, constrain the energy released in both bands, the geometry of the loops, and to study flares time evolution, we studied the brightest flares occurred in the 125‐Myr‐old stars in the Pleiades observed simultaneously with x‐ray multi‐mirror mission/Newton and Kepler/K2.