Probing Dark Contents in Globular Clusters With Timing Effects of Pulsar Acceleration

TL;DR

This paper studies pulsar timing residuals caused by accelerations in globular clusters, revealing potential signatures of dark remnants or black holes through timing effects and statistical analysis.

Contribution

It introduces a method to detect dark contents in globular clusters by analyzing pulsar timing residuals and constrains the mass of a potential central black hole in Terzan 5.

Findings

Timing residuals can indicate presence of black holes or dark remnants.

Maximum residual amplitude near cluster core is tens of nanoseconds.

Upper limit on central black hole mass in Terzan 5 is approximately 6000 solar masses.

Abstract

We investigate pulsar timing residuals due to the coupling effect of the pulsar transverse acceleration and the R$\rm{\ddot{o}}$mer delay. The effect is relatively small and usually negligible. Only for pulsars in globular clusters, it is possibly important. The maximum residual amplitude, which is from the pulsar near the surface of the core of the cluster, is about tens nanoseconds, and may hardly be identified for most of the globular clusters currently. However, an intermediate-mass black hole in the centre of a cluster can increase apparently the timing residual magnitudes. Particularly for the pulsars in the innermost core region, their residual magnitudes may be significant. The high-magnitude residuals, which above critical lines of each cluster, are strong evidences for the presence of a black hole or dark remnants of comparable total mass in the centre of the cluster. We also explored the timing effects of line-of-sight accelerations for the pulsars. The distribution of measured line-of-sight accelerations are simulated with a Monte Carlo method. A two-dimensional Kolmogorov-Smirnov tests are performed to reexamine the consistency of distributions of the simulated and reported data for various values of parameters of the clusters. It is shown that the structure parameters of Terzan 5 can be well constrained by comparing the distribution of measured line-of-sight accelerations with the distributions from Monte Carlo simulations. We provide that the cluster has an upper limit on the central black hole/dark remnant mass of $ \sim 6000 M_{\odot} $.