Is QSO1146+111B,C due to lensing by a cosmic string?

Abstract

A predicted consequence of cosmic strings is that they should produce equal-brightness double-lens images of distant quasars (QSOs), with separations of up to several minutes of arc (see refs 1, 2). Here I discuss a newly discovered lens candidate^3–6: QSO1146+111B,C which appears to consist of two images of equal brightness (B is 1.02 times as bright as C, with virtually identical spectra over the observed range) of a quasar at redshift z = 1.01, which are separated by 2.6 arc min. If this is produced by a cosmic string, its mass per unit length is µ⩾4.0×10²³ g cm⁻¹, a value large enough to be interesting for string-assisted galaxy formation^7–9 and near the upper limits implied by the isotropy of the cosmic microwave background^2,10 and constraints on gravitational radiation¹¹. But note that four other QSOs, also close enough to be double-imaged, have thus far not been detected. Searches for these and for the microwave background temperature shift across the string^2,10 would be useful.