http://arxiv.org/abs/1612.01793
We extend the model-independent approach to characterise strong gravitational lenses of \cite{bib:Wagner} to its most general form to leading order by using the orientation angles of a set of multiple images with respect to their connection line(s) in addition to the relative distances between the images, their ellipticities and time-delays. For two symmetric images that straddle the critical curve, the orientation angle additionally allows to determine the slope of the critical curve and a second (reduced) flexion coefficient at the critical point on the connection line between the images. It also allows to drop the symmetry assumption that the axis of largest image extension is orthogonal to the critical curve. For three images almost forming a giant arc, the degree of assumed image symmetry is also reduced to the most general case, allowing to describe image configurations for which the source need not be placed on the symmetry axis of the two folds that unite at the cusp. For a given set of multiple images, we set limits on the applicability of our approach, show which information can be obtained in cases of merging images, and analyse the accuracy achievable due to the Taylor expansion of the lensing potential for the fold case on a galaxy cluster scale NFW-profile. The position of the critical curve deviates from its true position up to 7\% of the relative distance between the images and the ratio of potential derivatives is retrieved within an accuracy of 22\% of the true value for images as far away from the critical curve as 40\% of the Einstein radius.
J. Wagner
Wed, 7 Dec 16
23/67
Comments: 8 pages, 6 figures, submitted to Astronomy and Astrophysics, comments welcome
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