We use the same notation for the generalized hypergeometric function as in the Mathematica package.

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Note that the theorem of the odd number of images (Schneider et al. 1992; Straumann 1998) does not apply here because the mass distribution is singular in the origin.

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... plane

Unless otherwise stated, $\log{x}$ is the logarithm base 10.

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... mass

Note that the value chosen for the mass of the BCG, though high, is not unrealistic. For instance, the estimated total mass of the Milky Way is $1.9_{-1.7}^{+3.6} \times 10^{12}~{M_{\odot}}$ (Wilkinson & Evans 1999) which is in the mass range we have adopted for the BCG.

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... axis

This is a consequence of having set $\vartheta_{\gamma} = 0$ . In general, the ellipse is elongated along the direction corresponding to $\vartheta_{\gamma}$ .

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... variable

Here, we denote with the subscript "e'' quantities referring to electrons, while the same quantities without subscripts refers to photons.

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