Local constraints on cosmic string loops from photometry and pulsar timing

We constrain the cosmological density of cosmic string loops using two observational signatures—gravitational microlensing and the Kaiser-Stebbins effect. Photometry from RXTE and CoRoT space missions and pulsar timing from Parkes Pulsar Timing Array, Arecibo and Green Bank radio telescopes allow us to probe cosmic strings in a wide range of tensions $G\mu /c^2={10}^{-16}÷{10}^{-10}$. We find that pulsar timing data provide the most stringent constraints on the abundance of light strings at the level ${\Omega }_s\sim {10}^{-3}$. Future observational facilities such as the Square Kilometer Array will allow one to improve these constraints by orders of magnitude.

Figure 1

The morphology of images and expected light curves for cosmic strings lensing a uniform brightness disk of various sizes. From upper-left to bottom-right $r/\delta$ is 0.2, 0.5, 2, 5. The positions of the string and the strip edges are shown by solid and dotted straight lines, respectively.

Figure 2

Pulsar timing residuals generated with the fake plugin of the tempo2 package [35]. The first picture shows 10 yr span of pulsar timing with $\sigma =150\mathrm{ns}$; the second one presents impact of string with $G\mu /c^2={10}^{-15}$ crossing at the fourth year of observations (timing noise omitted); the third one shows this impact on “real” pulsar with $\sigma =150\mathrm{ns}$.

Figure 3

Combined constraints on the average density of cosmic string loops based on CoRoT, RXTE, and PPTA data at $P=95\%$ level. One can see that pulsar timing currently provides the strongest constraints down to $G\mu /c^2\sim {10}^{-14}$ while lighter strings are constrained by the available data on Sco X-1; CoRoT data do not significantly constrain the population of loops at present.