http://arxiv.org/abs/1604.08339
In this work, we mainly study the magnification relations of quad lens models for cusp, fold and cross configurations. By dividing and ray-tracing in different image regions, we numerically derive the positions and magnifications of the four images for a point source lying inside of the astroid caustic. Then, based on the magnifications, we calculate the signed cusp and fold relations for the singular isothermal elliptical (SIE) lens. The signed fold relation map has positive and negative regions, and the positive region is usually larger than the negative region as has been confirmed before. It can explain that for many observed fold image pairs, the fluxes of the Fermat minimum images are apt to be larger than those of the saddle images. We define a new quantity cross relation which describes the magnification discrepancy between two minimum images and two saddle images. Distance ratio is also defined as the ratio of the distance of two saddle images to that of two minimum images. We calculate cross relations and distance ratios for nine observed Einstein cross type lensed samples. In theory, for most of the quad lens models, the cross relations decrease as the distance ratios increase. In observation, the cross relations of the nine samples do not agree with the quad lens models very well, nevertheless, the cross relations of the nine samples do not give obvious evidence for anomalous flux ratio as the cusp and fold types do. Then, we discuss several reasons for the disagreement, and expect good predictions from more precise observations and better lens models in the future.
Z. Chu, G. Li, W. Lin, et. al.
Fri, 29 Apr 16
54/57
Comments: 12 pages, 11 figures, submitted to MNRAS
You must be logged in to post a comment.