S2DFS: analysis of temporal changes of drifting subpulses

Context. We introduce a new technique, called the sliding two-dimensional fluctuation spectrum, used for detecting and characterising the temporal changes of drifting subpulses from radio pulsars. The method was tested using simulated data as well as archived observations made with the Westerbork Synthesis Radio Telescope (WSRT) at wavelengths of 92 and 21 cm. Aims. The drifting subpulse phenomenon is a well known property of radio pulsars. It has been studied extensively since their discovery, however the properties of the temporal behaviour of drifting subpulses are not fully explored. The drifting can also be non-coherent and the presence of effects like nulling or drift rate changing can mask the drifting behaviour of the pulsar. The S2DFS is a robust method for investigating this phenomenon and by introducing it we aim to expand our knowledge of the temporal drifting subpulse properties. Methods. Our new analysis method uses horizonally collapsed fluctuation spectra obtained with the two-dimensional fluctuation spectrum (2DFS) method. Stacking the collapsed spectra obtained in a 256 pulse window which slides by a pulse at a time produces a map of the collapsed fluctuation spectrum (S2DFS plot). By analysing the maps one can easily determine the presence of any temporal