S2DFS: analysis of temporal changes of drifting subpulses

Abstract

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 drift changes. Results. Simulated data showed that the technique can reveal the presence of any temporal changes in drift behaviour like mode changing or nulling. We have also analysed data of three pulsars, PSRs B0031−07, B1819−22 and B1944+17, which were selected based on the quality of the data and their known drift properties. All three sources are known to exhibit mode changes which could easily be seen in the S2DFS. Conclusions. The results from the analysis of the data sets used in this paper have shown that the S2DFS method is robust and complimentary to the 2DFS method in detecting and characterising the temporal changes in drifting subpulses from radio pulsars.

Investigation of the bi-drifting subpulses of radio pulsar B1839−04 utilising the open-source data-analysis project PSRSALSA

“…This provides the physical basis for different components having opposite drift senses. As pointed out by van Leeuwen & Timokhin (2012), the Ruderman & Sutherland (1975) model without the addition of an IAG does not necessarily imply that only one sense of carousel rotation is allowed. Therefore without invoking emission from the IAG, two nested beamlet systems rotating in opposite directions could be considered.…”

“…Nevertheless, we observe significant broadening. The variability of P 3 can be demonstrated more directly by exploiting the Sliding 2DFS (S2DFS; Serylak et al 2009), which has temporal resolution. The S2DFS is obtained by computing the 2DFS for separate blocks of data (here component II, for which both the modulation and intensity are strongest), where the block-size is n dft pulses of data.…”

“…6. See Serylak et al (2009) for a full description of the method. Figure 6 clearly shows mode changes between the Q mode (strong spectral power at P/P 3 = 0.08 cpp) and B mode (strong spectral power at lower frequencies).…”

A low frequency study of PSRs B1133+16, B1112+50, and B0031−07

“…The sliding two-dimensional fluctuation spectrum (S2DFS) was also computed to identify the onset of the various drift modes (Serylak et al 2009). The resulting plots from the LRMI, LRFS, and 2DFS analysis are shown in Fig.…”

Variations ofP2in subpulse drifting pulsars

“…Curved driftbands are common in radio pulsars that exhibit drifting subpulses (Edwards & Stappers 2003;Smits et al 2005;Serylak et al 2009;Hassall et al 2013). The "curvature" describes how P2 varies across the pulse window.…”