Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 53, p. 6-11 (2016)

Time delay of critical images of a point source near the gravitational lens fold-caustic

A. N. Alexandrov, Ph. D.,
V. I. Zhdanov, Dr. Sci.
Astronomical Observatory of Taras Shevchenko National University of Kyiv

Within the framework of the analytical theory of the gravitational lensing we derive asymptotic formula for the time delay of critical images of apoint source, which is situated near a fold-caustic. We found corrections of the first and second order in powers of a parameter, which describescloseness of the source to the caustic. Our formula modifies earlier result by Congdon, Keeton &Nordgren (MNRAS, 2008) obtained in zero-orderapproximation. We have proved the hypothesis put forward by these authors that the first-order correction to the relative time delay of two criticalmages is identically zero. The contribution of the corrections is illustrated in model example by comparison with exact expression.

The gravitational lens fold-caustic

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DOI: https://doi.org/10.17721/BTSNUA.2016.53.6-11