SIMBAD references

We use present theoretical estimates for the density of long cosmic strings to predict the number of strong gravitational lensing events in astronomical imaging surveys as a function of the angular resolution and survey area. We show that angular resolution is the single most important factor, and that interesting limits on the dimensionless string tension Gµ/c² can be obtained by existing and planned surveys. At the resolution of the Hubble Space Telescope (HST) (0.14arcsec), it is sufficient to survey of the order of a few square degrees - well within reach of the current HST archive - to probe the regime Gµ/c² ∼ 10^–7. If lensing by cosmic strings is not detected, such a survey would improve the limit on the string tension by a factor of two over that available from the cosmic microwave background. Future high resolution imaging surveys, covering a few hundred square degrees or more, either from space in the optical or from large-format radio telescopes on the ground, would be able to further lower this limit to Gµ/c² ∼ 10^–8. These limits will not be improved significantly by increasing the solid angle of the survey.