**Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 65, p. 22-26 (2022)**

**Effect of the source ellipticity on light curves in extragalactic gravitational lens systems**

**V. Zhdanov, Dr Hab., Prof.**

**Taras Shevchenko National University of Kyiv, Kyiv, Ukraine**

**Abstract**

Gravitational microlensing of elliptical sources in the linear caustic approximation is considered, based on the formula for the power-law distribution of brightness over the source plane; , where . This expression is convolved with the brightness amplification of the point source (linear caustic approximation). We have constructed the total amplification coefficients (amplification curves) that allow us to estimate the increase in the integral brightness of the source in microlensing processes for various orientations with respect to the linear caustic. The averaged amplification curves are built within the framework of a simplified statistical model when the source is crossed by linear caustics with an isotropic distribution of velocities (with fixed caustic strength and velocity modulus) , . The value of appears to be independent of the model parameter . The resulting estimates are qualitatively consistent with the conclusions obtained for the Gaussian source model, although there are differences related to the shape of the source brightness distribution. The results show that in view of the accuracy of the modern photometry, the effects of ellipticity are significant; however, they are obscured by other effects due to various conditions of a specific microlensing event. Moreover, registration of the ellipticity signal in real observations requires long-term monitoring with a large number of microlensing events.

**Key words
**Gravitational lenses, microlensing, elliptical source, light curves.

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