Extreme-ultraviolet multi-wavelength observations of quasi-periodic pulsations in a solar post-flare cusp-shape loop with SDO/AIA

We present extreme-ultraviolet multi-wavelength observations with the SDO/AIA instruments of quasi-periodic pulsations (QPPs) propagating along a cusp-shaped loop formed after an M2.2 flare on the Sun. Our motivation is to detect whether there were slow-mode magnetoacoustic waves propagating along its protruding flux tube. To this end, with fast Fourier transform we extract the short (<3minutes) and long (>3minutes) period components of the QPPs from time-space diagrams of the tube slices. We find that velocity differences did exist among the short/long-period components of different wavelengths, but only one event in the long-period ones showed they were greater than the measurement errors (e.g., 65kms^-1), which were 330kms^-1 detected in 171 Å, 590kms^-1 in 211 Å, and 180kms^-1 in 304 Å. The intensity modulation in all wavelengths is found to be very large, e.g., ∼60% of the emission trend for an event in the 171 Å passband, which would be an order of magnitude higher than the perturbation of the plasma density in the slow-mode magnetoacoustic waves. Moreover, only the QPPs with upward velocities of 50-300kms^-1 are found in the tube, and the downward ones of several tens of kilometers are never unambiguously detected. Therefore, most of the QPP events under study were likely the episodic outflows along the tube, and the one with a supersonic speed of 590kms^-1 may be a kink wave.