|Description:|| The latest LOFAR paper, "Differential Frequency-dependent Delay from the Pulsar Magnetosphere" (Hassall et al. 2013) has recently been accepted for publication in A&A. |
In the paper, we use LOFAR to observe single pulses ("subpulses") from the bright pulsar B0809+74. In many pulsars, subpulses are seen to "drift" through the average pulse profile - moving to earlier pulse phase with each successive pulse period, however the drifting pattern seen in B0809+74 is much more complex. At low frequencies subpulses drift almost linearly through the pulse profile but above 610 MHz, the drifting pattern becomes disrupted, and there is a subpulse phase step, where the path of the subpulses through the pulse profile seems to jump suddenly.
From LOFAR low band data, we show that the pulse profile is actually composed of two components, both of which have separate driftbands associated with them. At high frequencies, the components (and their driftbands) overlap, and it is the conjunction between the driftbands which gives rise to the subpulse phase step. The shape of the pulse profile, and the manner in which it evolves with observing frequency cannot be explained by current models of the pulsar magnetosphere, and hint that extra effects (such as refraction) are required to explain what we observe.