A 50-min coronal kink oscillation and its possible photospheric counterpart

Abstract: A coronal loop of 290~Mm length, observed at 171~\AA\ with SDO/AIA on February 6th 2024 near AR 13571, is found to oscillate with two significantly different oscillation periods, $48.8 \pm 6.1$~min and $4.8\pm 0.3$~min. The oscillations occur in the time intervals without detected flares or eruptions. Simultaneously, near the Northern footpoint of the oscillating loop, we detect a $49.6 \pm 5.0$-min periodic variation of the average projected photospheric magnetic field observed with SDO/HMI. The shorter-period decayless oscillation is attributed to the eigen-mode, standing kink oscillation of the loop, while the longer-period oscillation may be the oscillatory motion caused by the periodic footpoint driver. The photospheric long-period process can also drive the short-period, eigen oscillation of the loop via the self-oscillatory, \lq\lq violin\rq\rq\, mechanism, in which a transverse oscillation is excited by an external quasi-steady flow. This finding indicates that the most powerful, lower-frequency spectral components of photospheric motions, which are well below the Alfv\'enic/kink cutoff, can reach the corona.