Probing dark contents in globular clusters with timing effects of pulsar acceleration

Abstract

Abstract We investigate pulsar timing residuals due to the coupling effect of the pulsar transverse acceleration and the Römer 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 of nanoseconds, and may hardly be identified for most globular clusters currently. However, an intermediate-mass black hole in the center of a cluster can apparently increase the timing residual magnitudes. Particularly for pulsars in the innermost core region, their residual magnitudes may be significant. The high-magnitude residuals, which are above critical lines of each cluster, are strong evidence for the presence of a black hole or dark remnants of comparable total mass in the center 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. 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 constrained well by comparing the distribution of measured line-of-sight accelerations with the distributions from Monte Carlo simulations. We find that the cluster has an upper limit on the central black hole/dark remnant mass of ∼ 6000 M ⊙.