The selected post-doc will perform a pioneering ultra-low-frequency study of radio millisecond pulsars (MSPs) with LOFAR. MSPs form the core of Pulsar Timing Arrays (PTAs), which hold the promise of making the first direct detection of gravitational waves. With LOFAR, we will measure steep frequency-dependent effects caused by propagation of the signal through the interstellar medium (e.g. dispersion and scattering), as well as frequency-dependent changes in the pulse-profile morphology.Since these effects are by far largest at low frequencies, these observations can detect effects too subtle to be easily seen at higher radio frequencies but which still affect timing at the precision necessary to detect gravitational waves (< 100 ns). We will use the information gathered at low frequencies to improve the precision with which pulsars can be timed at higher frequencies, with the primary goal of increasing the sensitivity of PTAs.

The time is ripe for such studies, and LOFAR is the most powerful and versatile low-frequency radio telescope ever constructed. With the current boom in the number of MSP discoveries, there are now also more sources than ever to study, and the best new timers are being incorporated into PTAs. Though largely sensitivity limited until now, PTAs are hitting the point where timing errors are dominated by these un-modeled systematics (e.g. propagation and jitter). With the SKA on the horizon, a complete understanding of these effects will be crucial for reaping the full advantage that a huge increase in sensitivity will have for pulsar timing precision.