Fitting gravitational lenses: truth or delusion

Evans, N. W.; Witt, Hans J.

doi:10.1046/j.1365-2966.2003.07057.x

Cited by 82 publications

(120 citation statements)

References 66 publications

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“…It still has to be investigated how critical the SPT could be for sources observed at those resolutions if substructures are not explicitly included in the lens models and/or if reasonable freedom is allowed regarding the angular structure of the lens (e.g. Evans & Witt 2003;Saha & Williams 2006). Nevertheless, the expected substructure and line-of-sight inhomogeneities mentioned above will put a lower limit to the positional accuracy at which lens systems can be modeled with smooth matter distributions.…”

Section: Discussionmentioning

confidence: 99%

“…For example, a four-image system provide a total of six positional constraints on the lensing mass distribution, and many different density profiles can satisfy these constraints. The variety of mass distribution that can reproduce a set of lensed images can be seen by adding angular structures to the lens potential (Trotter et al 2000;Evans & Witt 2003), or by modeling the mass distribution with a grid of variable pixels or a sum of basis functions (e.g. Saha & Williams 1997;Diego et al 2005;Coe et al 2008;Liesenborgs & De Rijcke 2012).…”

Section: Introductionmentioning

confidence: 99%

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Source-position transformation: an approximate invariance in strong gravitational lensing

Schneider

Sluse

2014

A&A

149

146

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The main obstacle that gravitational lensing has in determining accurate masses of deflectors, or in determining precise estimates for the Hubble constant, is the degeneracy of lensing observables with respect to the mass-sheet transformation (MST). The MST is a global modification of the mass distribution which leaves all image positions, shapes, and flux ratios invariant, but which changes the time delay. Here we show that another global transformation of lensing mass distributions exists which leaves image positions and flux ratios almost invariant, and of which the MST is a special case. As is the case for the MST, this new transformation only applies if one considers only those source components that are at the same distance from us. Whereas for axi-symmetric lenses this source position transformation exactly reproduces all strong lensing observables, it does so only approximately for more general lens situations. We provide crude estimates for the accuracy with which the transformed mass distribution can reproduce the same image positions as the original lens model, and present an illustrative example of its performance. This new invariance transformation is most likely the reason why the same strong lensing information can be accounted for with rather different mass models.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Source-position transformation: an approximate invariance in strong gravitational lensing

Schneider

Sluse

2014

A&A

149

146

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“…KGP05 or Rozo et al 2005 for a recent extensive summary of the situation). Indeed, from a lensing perspective, flux ratios are not only sensitive to substructures but also to m = 3 and m = 4 multipoles of the lens model (Evans & Witt 2003;Möller et al 2003;Quadri et al 2003;Kawano et al 2004), to the lens environment (Oguri 2005), to the source size (Dobler & Keeton 2005;Chiba et al 2005) and to isolated dark matter clumps on the same line of sight (Chen et al 2003;Metcalf 2005a,b;Wambsganss et al 2005). From a hydrodynamical simulation perspective, the expected amount of dark matter within the Einstein radius of a lens is not well known.…”

Section: Anomalous Flux Ratiosmentioning

confidence: 99%

Multi-wavelength study of the gravitational lens system RXS J113155.4-123155

Sluse

Claeskens²,

Altiéri

et al. 2006

A&A

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Aims. RXS J113155.4-123155 (z = 0.66) is a quadruply imaged lensed quasar with a resolved Einstein Ring. The goal of this paper is to provide a full characterization of this system, and more particularly accurate astrometry and photometry. These observational constraints constitute a mandatory ingredient for the precise determination of the lens mass profile, the derivation of the Hubble constant H 0 from time delay measurements and investigations on the presence of massive substructures in the lensing galaxy. Methods. Visible and near-infrared imaging observations of RXS J113155.4-123155 were carried out at various epochs using several ground based telescopes and the HST. The frames have been deconvolved using the MCS algorithm. A Singular Isothermal Ellipsoid (SIE) + external shear has been used to model the lensing galaxy potential. Results. MCS deconvolution enables us to separate the flux of the QSO (point-like images) from that of its host galaxy and to accurately track the flux variations of the point-like images in various filters. The deconvolved frames unveil several multiply imaged structures in the Einstein ring and an unidentified object in the vicinity of the lensing galaxy. We discuss the lightcurves and the chromatic flux ratio variations and deduce that both intrinsic variability and microlensing took place during a span longer than one year. We demonstrate that microlensing may easily account for the so called anomalous flux ratios presented in the discovery paper. However, the observed flux ratios are still poorly reproduced when modeling the lens potential with a SIE+shear. We argue that this disagreement can hardly be explained by milli-lensing caused by substructures in the lensing galaxy. A solution proposed in Paper II consists in a more complex lens model including an octupole term to the lens gravitational potential.

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“…This discrepancy may have several origins such as invalid assumption about the lens model, i.e. a need for multipole components (Evans & Witt 2003), microlensing, and/or massive substructures in the lensing galaxies (see Keeton et al 2003Keeton et al , 2005, for an exhaustive discussion).…”

Section: Quads and Astrometric Anomaliesmentioning

confidence: 99%

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Chantry¹,

Sluse²,

Magain³

2010

A&A

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Aims. We attempt to place very accurate positional constraints on seven gravitationally lensed quasars currently being monitored by the COSMOGRAIL collaboration, and shape parameters for the light distribution of the lensing galaxy. We attempt to determine simple mass models that reproduce the observed configuration and predict time delays. We finally test, for the quads, whether there is evidence of astrometric perturbations produced by substructures in the lensing galaxy, which may preclude a good fit with the simple models. Methods. We apply the iterative MCS deconvolution method to near-IR HST archival data of seven gravitationally lensed quasars. This deconvolution method allows us to differentiate the contributions of the point sources from those of extended structures such as Einstein rings. This method leads to an accuracy of 1-2 mas in the relative positions of the sources and lens. The limiting factor of the method is the uncertainty in the instrumental geometric distortions. We then compute mass models of the lensing galaxy using state-of-the-art modeling techniques. Results. We determine the relative positions of the lensed images and lens shape parameters of seven lensed quasars: HE 0047-1756, RX J1131-1231, SDSS J1138+0314, SDSS J1155+6346, SDSS J1226-0006, WFI J2026-4536, and HS 2209+1914. The lensed image positions are derived with 1-2 mas accuracy. Isothermal and de Vaucouleurs mass models are calculated for the whole sample. The effect of the lens environment on the lens mass models is taken into account with a shear term. Doubly imaged quasars are equally well fitted by each of these models. A large amount of shear is necessary to reproduce SDSS J1155+6346 and SDSS J1226-006. In the latter case, we identify a nearby galaxy as the dominant source of shear. The quadruply imaged quasar SDSS J1138+0314 is reproduced well by simple lens models, which is not the case for the two other quads, RX J1131-1231 and WFI J2026-4536. This might be the signature of astrometric perturbations caused by massive substructures in the galaxy, which are unaccounted for by the models. Other possible explanations are also presented.

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Fitting gravitational lenses: truth or delusion

Cited by 82 publications

References 66 publications

Source-position transformation: an approximate invariance in strong gravitational lensing

Source-position transformation: an approximate invariance in strong gravitational lensing

Multi-wavelength study of the gravitational lens system RXS J113155.4-123155

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

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