paper

Generalised model-independent characterisation of strong gravitational lenses V: reconstructing the lensing distance ratio by supernovae for a general Friedmann universe

arXiv:1812.04002 · doi:10.1093/mnras/stz2717

Abstract

We determine the cosmic expansion rate from supernovae of type Ia to set up a data-based distance measure that does not make assumptions about the constituents of the universe, i.e. about a specific parametrisation of a Friedmann cosmological model. The scale, determined by the Hubble constant , is the only free cosmological parameter left in the gravitational lensing formalism. We investigate to which accuracy and precision the lensing distance ratio is determined from the Pantheon sample. Inserting and its uncertainty into the lensing equations for given , esp. the time-delay equation between a pair of multiple images, allows to determine lens properties, esp. differences in the lensing potential (), without specifying a cosmological model. We expand the luminosity distances into an analytic orthonormal basis, determine the maximum-likelihood weights for the basis functions by a globally optimal -parameter estimation, and derive confidence bounds by Monte-Carlo simulations. For typical strong lensing configurations between and , can be determined with a relative imprecision of 1.7%, assuming imprecisions of the time delay and the redshift of the lens on the order of 1%. With only a small, tolerable loss in precision, the model-independent lens characterisation developed in this paper series can be generalised by dropping the specific Friedmann model to determine in favour of a data-based distance ratio. Moreover, for any astrophysical application, the approach presented here, provides distance measures for that are valid in any homogeneous, isotropic universe with general relativity as theory of gravity.

16 pages, 4 figures, accepted for publication in MNRAS, comments welcome

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