D. R. Madison, S. Chatterjee, J. M. Cordes
Precisely measured astrometric parameters are integral to successful pulsar timing campaigns. They are commonly measured by fitting the astrometric parameters of a deterministic timing model to a series of pulse times of arrival (TOAs). TOAs measured to microsecond precision over several-year spans can in this way provide astrometric parameters precise to sub-milliarcsecond levels. However, pulsars do not pulsate in a deterministic fashion. Many display significant amounts of red spin noise. Furthermore, a stochastic background of gravitational waves can lead to red noise-like structure in TOAs. We investigate how noise of different spectral types is absorbed by timing models and leads to significant estimation errors in the astrometric parameters. Independent of timing, very long baseline interferometry (VLBI) is capable of providing sub-milliarcsecond astrometric parameters for pulsars. We find that incorporating VLBI astrometric measurements into the timing models of pulsars for which only a couple of years of timing data exist will lead to more realistic assessments of red spin noise, yield more accurate astrometric parameters, and could enhance the amplitude of certain gravitational wave signatures in post-fit timing residuals by factors of 20 or more.
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http://arxiv.org/abs/1210.2469
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