Compressive Oscillations in Hot Coronal Loops: Are Sloshing Oscillations and Standing Slow Waves Independent?

Employing high-resolution EUV imaging observations from SDO/AIA, we analyze a compressive plasma oscillation in a hot coronal loop triggered by a C-class flare near one of its footpoints, as first studied by Kumar et al. We investigate the oscillation properties in both the 131 angstrom and 94 angstrom channels and find that what appears as a pure sloshing oscillation in the 131 angstrom channel actually transforms into a standing wave in the 94 angstrom channel at a later time. This is the first clear evidence of such transformation and confirms the results of a recent numerical study that suggests that these two oscillations are not independent phenomena. We introduce a new analytical expression to properly fit the sloshing phase of an oscillation and extract the oscillation properties. For the AIA 131 angstrom channel, the obtained oscillation period and damping time are 608 +/- 4 s and 431 +/- 20 s, respectively, during the sloshing phase. The corresponding values for the AIA 94 angstrom channel are 617 +/- 3 s and 828 +/- 50 s. During the standing phase that is observed only in the AIA 94 angstrom channel, the oscillation period and damping time have increased to 791 +/- 5 s and 1598 +/- 138 s, respectively. The plasma temperature obtained from the differential emission measure analysis indicates substantial cooling of the plasma during the oscillation. Considering this, we show that the observed oscillation properties and the associated changes are compatible with damping due to thermal conduction. We further demonstrate that the absence of a standing phase in the 131 angstrom channel is a consequence of cooling plasma besides the faster decay of oscillation in this channel.