Detection of ultra-long-period oscillations in an EUV filament

We report the first detection of long-period (8-27 h) oscillatory intensity variations in a coronal filament. The filament is observed continuously as it crosses the solar disk in a 12-min-cadence SoHO/EIT 195 Å uninterrupted data set. Cyclic intensity variations are found to be correlated along the filament, while the most pronounced oscillations are detected at its southern end for nearly 6 days. The dominant period of these oscillations is 12.1 h and the amplitude of the intensity variations reaches approximately 10% of the background intensity. The ultra-long-period oscillations may be interpreted in terms of slow string MHD modes or may be connected with thermal over-stability associated with peculiarities of the cooling/heating function and with the effect of neutrals. These theoretical predictions however do not explain the spatial structure of the oscillations along the filament.