Shapiro effect as a possible cause of the low-frequency pulsar timing noise in globular clusters |
| |
| Authors: | T I Larchenkova S M Kopeikin |
| |
| Institution: | (1) Astrospace Center, Lebedev Physical Institute, Russian Academy of Sciences, Profsoyuznaya ul. 84/32, Moscow, 117997, Russia;(2) Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, MO 65211, USA |
| |
| Abstract: | A prolonged timing of millisecond pulsars has revealed low-frequency uncorrelated (infrared) noise, presumably of astrophysical
origin, in the pulse arrival time (PAT) residuals for some of them. Currently available pulsar timing methods allow the statistical
parameters of this noise to be reliably measured by decomposing the PAT residual function into orthogonal Fourier harmonics.
In most cases, pulsars in globular clusters show a low-frequency modulation of their rotational phase and spin rate. The relativistic
time delay of the pulsar signal in the curved spacetime of randomly distributed and moving globular cluster stars (the Shapiro
effect) is suggested as a possible cause of this modulation. Extremely important (from an astrophysical point of view) information
about the structure of the globular cluster core, which is inaccessible to study by other observational methods, could be
obtained by analyzing the spectral parameters of the low-frequency noise caused by the Shapiro effect and attributable to
the random passages of stars near the line of sight to the pulsar. Given the smallness of the aberration corrections that
arise from the nonstationarity of the gravitational field of the randomly distributed ensemble of stars under consideration,
a formula is derived for the Shapiro effect for a pulsar in a globular cluster. The derived formula is used to calculate the
autocorrelation function of the low-frequency pulsar noise, the slope of its power spectrum, and the behavior of the σz statistic that characterizes the spectral properties of this noise in the form of a time function. The Shapiro effect under
discussion is shown to manifest itself for large impact parameters as a low-frequency noise of the pulsar spin rate with a
spectral index of n = −1.8 that depends weakly on the specific model distribution of stars in the globular cluster. For small impact parameters,
the spectral index of the noise is n = −1.5. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
