摘要：We develop a new approach to extracting model-independent information from observations
of strong gravitational lenses. The approach is based on the generic properties of images
near the fold and cusp catastrophes in caustics and critical curves. The observables we
used are the relative image positions, the magnification ratios and ellipticities of
extended images, and time delays between images with temporally varying intensity. We show
how these observables constrain derivatives and ratios of derivatives of the lensing
potential near a critical curve. Based on these measured properties of the lensing
potential, classes of parametric lens models can then easily be restricted to the
parameter values that are compatible with the measurements, thus allowing fast scans of a
large variety of models. Applying our approach to a representative galaxy (JVAS B1422+231)
and a galaxy-cluster lens (MACS J1149.5+2223), we show which model-independent information
can be extracted in each case and demonstrate that the parameters obtained by our approach
for known parametric lens models agree well with those found by detailed model
fitting.
关键词：dark matter;gravitational lensing: strong;methods: data analysis;methods: analytical;galaxies: clusters: general;galaxies: luminosity function, mass function
