Erratum for: A&A 580, A79 (2015), DOI: 10.1051/0004-6361/201526773

The authors would like to point out two errors in the article as it was originally published.

Due to a typographical error, Eq. (17) erroneously expresses the shear of the elliptical power law profile lens in the elliptic coordinates R and ϕ instead of the physical polar coordinates r and θ. The correct expression is $\mathit{\gamma }\mathrm{\left(}\mathit{r,\theta }\mathrm{\right)}\mathrm{=}\mathrm{-}{\mathrm{e}}^{\mathrm{i}\mathrm{2}\mathit{\theta }}\hspace{0.17em}\mathit{\kappa }\mathrm{\left(}\mathit{r}\mathrm{\right)}\mathrm{+}\mathrm{(}\mathrm{1}\mathrm{-}{\mathit{t}}^{\mathrm{)}}{\mathrm{e}}^{\mathrm{i}\mathit{\theta }}\hspace{0.17em}\frac{\mathit{\alpha }\mathrm{\left(}\mathit{r,\theta }\mathrm{\right)}}{\mathit{r}}\mathit{,}$(17) i.e. the same formula with the substitutions R → r and ϕ → θ. This result correctly recovers the singular isothermal ellipsoid result γ = − κ (z/z^⋆) = − e^i2θκ when t = 1. The preceding Eq. (16) is correct.

Furthermore, Fig. 2 incorrectly contains and refers to the pseudo-caustics for power law profile lenses with slope t> 1. Since the main result of the original paper shows that the elliptical lenses have the same (elliptical) radial profile as the circular ones, the degenerate critical line at the origin R = 0 is mapped to R = ∞ when t> 1, just as in the circular case. Hence only the isothermal case t = 1 has a pseudo-caustic at finite radius. The dashed lines in the plot are due to a numerical error. A corrected version of Fig. 2 is shown below.

Fig. 2 Critical lines (black) and caustics (grey) of the elliptical power law profile lens. Also shown is an ellipse with semi-minor axis equal to the scale length b and axis ratio q (red, dotted). For the purpose of illustration, the scale length b decreases as q1/2. The slope of the power law profile varies from t = 0.25 (left) to t = 1.75 (right) in steps of 0.5. The axis ratio varies from q = 0.8 (top) to q = 0.2 (bottom) in steps of 0.2.

Acknowledgments

The authors thank Yiping Shu and Massimo Meneghetti for their careful reading of the original article.

© ESO 2016

All Figures

Fig. 2 Critical lines (black) and caustics (grey) of the elliptical power law profile lens. Also shown is an ellipse with semi-minor axis equal to the scale length b and axis ratio q (red, dotted). For the purpose of illustration, the scale length b decreases as q1/2. The slope of the power law profile varies from t = 0.25 (left) to t = 1.75 (right) in steps of 0.5. The axis ratio varies from q = 0.8 (top) to q = 0.2 (bottom) in steps of 0.2.

In the text