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Furlanetto extend the usual elliptically-symmetric Sersic model for source galaxies to make the major axis a segment of a circle and the ellipse into an "ArcEllipse". They then explore ways of fitting this to pixelated, blurry data, and compromise on a method that underestimates flux but captures (quickly) the L/W ratio found by other methods. Since they base their measurements on SExtractor segmented images, this parameterisation could be adopted by Gavazzi et al's RingFinder code (if something equivalent is not already implemented). Interestingly, the number of parameters needed to specify an ArcEllipse is the same as that needed for a Sersic lensed by an SIS+Shear lens, though the predicted arc surface brightness is different.

Still reading the paper but... I remember that I talked to E. Bertin about how efficient SExtractor is to segment arc-like images. He was very negative about this. I'd like to hear your opinion on that!

In my experience SExtractor can do a very nice job at segmenting arcs. The tricky part is finding a SExtractor setup that works for arcs of all shapes, sizes and surface brightnesses. You can certainly bias your sample by choosing one setup over another. This is just a variant of the usual astronomical dynamic range problem of course - all methods have to solve this.

Would be nice to make similar forecast for Euclid (~40 epochs in the Deep Caps)

Collett et al are attempting to use all the information in the galaxy catalog for the field around a strong lens (well, the stellar masses and photometric redshifts, at least) in order to reconstruct, using a halo model, the external convergence at the lens (like Wong, Keeton et al have been doing). In fact, their code (Pangloss) returns the PDF Pr(kappa|data), which can then be propagated into a time delay distance measurement. The model is pretty simple right now, and so everything has to be calibrated to N-body simulations (not dissimilarly from how the Suyu/COSMOGRAIL "H0LiCoW" group have been treating this problem in B1608 and RXJ1131). The goal for the future is to break free of this calibration by increasing the flexibility and physical realism of the mass model.

Formed in summer 2012, the LSST DESC sets out its plans for the next few years, preparing to try and measure the accelerating expansion of the Universe very accurately indeed. Most of the work between now and 2020 will be on trying to predict, understand and mitigate against systematic errors in this measurement - so analysis pipelines need defining, implementing (in pieces) and testing on simulations. The strong lensing case is primarily time delay distances from ~1000 lensed quasars and SNe, but multiple source plane systems could play a role as well.