1. Project P2445 – Four-Frequency High Precision Timing of a Millisecond Pulsar Ryan Shannon (PI, Graduate Student, Cornell University), with Jim Cordes, Paul Demorest, David Nice, Joe Lazio, and Dan Stinebring. The detection of gravitational waves with pulsars will requires high timing precision: effects at 10 ns level can limit the sensitivity to gravitational waves. ISM acts like warped glass, distorting the trajectory of the propagating radio waves (tube). As the volume of interstellar space changes, the tube wanders, resulting in arrival time variations. Goals of project: Identify and mitigate the effect of variability in the interstellar medium (interstellar weather) in precision pulsar timing observations and develop these effects. Radio waves travel through banana- shaped tube Tube size Pulsar Earth Solar System Barycentre Tube offset from direct line-of-sight

2. PSR J1713+0747: Most stable millisecond pulsar in Arecibo declination Range. Observations: 327 MHz, 430 MHz, L and S bands. 20 transits over 6 months. Recorded data simultaneously with backends suitable for timing (ASP, high time resolution) and ISM analysis (WAPP higher frequency resolution), and a baseband recorder (Mark5). L-band observations, systematic trends (associated with ISM?) S-band observations, lower timing precision due to lower flux. Combine all TOAs to form “grand” arrival time at this epoch ~ 2 hours ~1 microsec

3. Key Analysis: Connect residual times of arrival (top) and pulsar dynamic spectra and determine if the dynamic spectra encode ISM delays? 430 MHz 327 MHz

4. Project in progress: (Ryan’s dissertation: coming in August 2010!) Requirements for mitigating ISM effects: Wide bandwidth instrumentation: ISM effects are mitigated by both a) observing at higher frequencies and b) observing with wider bandwidths. Also require instruments with high frequency resolution to perform dynamic spectra analysis (i.e., Mock) complementary to wide bandwidth timing instruments (GUPPI-clone). Need sensitive telescope (i.e. Arecibo) to identify and mitigate propagation effects Ryan would like to thank the AO Staff (especially Tapasi Ghosh) for assistance with the observations 6 months The 10000 ASP Times of Arrival