Using PSR J0437-4715 To Study The Variability Of The Gravitational Constant And Clock Jumps

Pulsars are a kind of compact objects and spin stably,which make them closely connect to the theory of gravity and time scale.PSR J0437-4715 is one of the most stable and timed pulsars.It is in a binary system and companied with a white dwarf.The thesis describes two aspects of the study by observing PSR J0437-4715 with Kunming 40-m radio telescope at Yunnan observatories1.Using VLBI,we found two in-beam reference sources for PSR J0437-4715,which can be used to obtain the parallax at 10-mas error.It will be the most precise measure-ment to PSR J0437-4715,which is five-times better than the current measurement.Com-bining with the kinematic distance,the high-precision parallax distance of PSR J0437-4715 can be used to constrain the variability of the gravitational constant,G/G.G/G contains important information about our cosmology,gravitational theory and even all of the fundamental constants in physics.The upper limit of the G' s variability can be obtained by the difference between the kinematic distance and parallax distance.Based on it,Deller et al.obtained a precise measurement using PSR J0437-4715.However,the large angular distance between the reference source and PSR J0437-4715 limits their parallax measurement by 50 uas.We found two radio sources in PSR J0437-4715' s 1 arcmin radius by re-reduce the VLA archive that observed in the year 1996.To confirm the sources are proper for ref-erencing PSR J0437-4715,we observed them with LB A and KM40m telescope.The re-sults showed:(1)still detectable in our observation;(2)with compact structure;(3)brightness temperatures are no less than 10E7 Kelvin.In addition,we obtained more information from the ATCA and VLA data:(4)always detectable in recent 20-years;(5)the indices of variability are less than 0.15;(6)radio spectra are flat.Moreover,we found no counter-part in other electromagnetic bands.So,we argue that they are most probably compact AGN cores outside our Galaxy.They have stable position and stable flux,which make them ideal reference sources.2.Using the timing data of PSR J0437-4715 and some other pulsars,we measured the clock jumps of the observational system.And the 600 us-error residuals gave 80ns-precision measurement,the precision is already comparable to the commercial time service.Meanwhile,the method can be used to estimate the lowest order of the clock waveform,which is fundamental to constructing the pulsar time scalePulsar timing is the key technique to utilize the stability of pulsars.Almost all the physical information can be found in the timing residuals.Precise timing needs the clock signal to be coherent and stable.But for long-term case,the clocks at station will inevitably encounter aberrations that should be deal with for precise timing.And,the clock jumps are the most obvious aberrations.Because clock jumps can be directly showed in residuals,residuals can give the jumps inversely.we investigated the statis-tical signal-processing algorithm to measure the clock jumps from the timing data of multiple pulsars including PSR J0437-4715.Our algorithm is based on the framework of Bayesian statistics.In order to make the Bayesian algorithm applicable with lim-ited computational resources,we dedicated our efforts to the analytic marginalization of irrelevant parameters.We found that the widely used parameter for pulsar timing systematics,the 'Efac' parameter,can be analytically marginalized.This reduces the Gaussian likelihood to a function very similar to the Student' s t-distribution.Our iter-ative method to solve the maximum likelihood estimator is also explained in the thesis.