We investigate the validity of the approximate method to describe a strong gravitational lensing which was extended by Alard on the basis of a perturbative approach to an Einstein ring. Adopting an elliptical NavarroFrenkWhite (NFW) lens model, we demonstrate how the approximate method works, focusing on the shape of the image, the magnification, caustics, and the critical line. Simplicity of the approximate method enables us to investigate the lensing phenomena in an analytic way. We derive simple approximate formulas which characterize a lens system near the Einstein ring.
All Science Journal Classification (ASJC) codes
- Mathematical Physics
- Astronomy and Astrophysics
- Space and Planetary Science