http://arxiv.org/abs/1711.08386
The frequencies and phases of emission from extra-solar sources, as measured by Earth-bound observers, are modulated due to the Doppler motions of the observer with respect to the source, and through relativistic effects. These modulations depend critically on the sky-location of the source. Precise knowledge of the modulations is required if wanting to coherently track the phase of a source over long observation times, for example in pulsar timing, or searches for continuous gravitational wave sources. The modulations can be modelled as a sky-location and time dependent time delay that converts arrival times at the observer to the inertial frame of the source. In many cases this inertial frame can be the solar system barycentre (SSB). We study the use of Reduced Order Modelling for speeding up the calculation of the time delay between an observer and the SSB for any sky-location and for coherent observations spanning one year. We find that the time delay model can be decomposed into just four basis vectors, which can be used to reconstruct the time delay for any sky-location to sub-nanosecond accuracy. When compared to the standard routines for time delay calculation used in gravitational wave searches, the use of the reduced basis can lead to a speed-up factor of 30 times. We have also studied the components of equivalent time delays for sources in binary systems. For these, assuming eccentricities less than 0.25, we can reconstruct the delays to within 100s of nanoseconds, with best case speed-ups of a factor of 10, or factors of two when having to interpolate the basis to different orbital periods or time stamps. In long-duration phase-coherent searches for sources with large sky-position uncertainties, or binary parameter uncertainties, these speed-ups could allow enhancements in their scopes without large additional computational burdens.
M. Pitkin, S. Doolan, L. McMenamin, et. al.
Thu, 23 Nov 17
44/52
Comments: 11 pages, 8 figures