Asymptotic formulas for the magnification of a gravitational lens system near a fold caustic |
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| Authors: | A N Alexandrov V I Zhdanov E V Fedorova |
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| Institution: | 1.Astronomical Observatory,Taras Shevchenko Kiev National University,Kiev,Ukraine |
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| Abstract: | An approximate formula for the magnification of a point source near a fold caustic obtained in the first linear caustic approximation
is widely used in the theory of gravitational lens systems. Here, this formula is refined to include the post-linear terms
that have been found both for a point source and for an extended Gaussian source in the absence of continuous matter on the
line of sight. The formulas are reduced to a form containing three additional parameters; the derivation of nontrivial corrections
requires including the expansion terms in the lens equation up to the fourth order. The modified formula for an extended source
is used to analyze strong microlensing events in the gravitational lens system Q2237+0305 (the Einstein Cross). For such an
event on the light curve of image C (1999, OGLE data), the corrections found are statistically significant. |
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