[show abstract][hide abstract] ABSTRACT: We analyse the timing residuals for 50 pulsars observed using the Nanshan 25-m radio telescope at Urumqi Observatory by determining the Hurst parameter for each data set using the rescaled range method. These pulsars have been observed over a time span of 5–8 yr and have been selected to have timing residuals that resemble white noise rather than smooth curves. The results are compared with those for shuffled residual series. Despite the noise-like appearance, some timing residual series showed Hurst parameters that deviated significantly from the shuffled series. We conclude that Hurst parameter analysis is capable of detecting long-term memory in timing residuals.
Monthly Notices of the Royal Astronomical Society 04/2011; 412(4):2678 - 2684. · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: It is still a matter of debate to understand the equation of state of cold supra-nuclear matter in compact stars because of unknown on-perturbative strong interaction between quarks. Nevertheless, it is speculated from an astrophysical view point that quark clusters could form in cold quark matter due to strong coupling at realistic baryon densities. Although it is hard to calculate this conjectured matter from first principles, one can expect the inter-cluster interaction to share some general features to nucleon-nucleon interaction. We adopt a two-Gaussian component soft-core potential with these general features and show that quark clusters can form stable simple cubic crystal structure if we assume Gaussian form wave function. With this parameterizing, Tolman-Oppenheimer-Volkoff equation is solved with reasonable constrained parameter space to give mass-radius relation of crystalline solid quark star. With baryon densities truncated at 2 times nuclear density at surface and range of interaction fixed at 2fm we can reproduce similar mass-radius relation to that obtained with bag model equations of state. The maximum mass ranges from about 0.5 to 3 solar mass. Observed maximum pulsar mass (about 2 solar mass) is then used to constrain parameters of this simple interaction potential. Comment: 5 pages, 2 figures
[show abstract][hide abstract] ABSTRACT: We present an analysis of timing residual (noise) of 54 pulsars obtained from 25-m radio telescope at Urumqi Observatory with a time span of 5~8 years, dealing with statistics of the Hurst parameter. The majority of these pulsars were selected to have timing noise that look like white noise rather than smooth curves. The results are compared with artificial series of different constant pairwise covariances. Despite the noise like appearance, many timing residual series showed Hurst parameters significantly deviated from that of independent series. We concluded that Hurst parameter may be capable of detecting dependence in timing residual and of distinguishing chaotic behavior from random processes. Comment: 7 pages, 3 figures, 2 tables, Submitted to MNRAS