Results of optical monitoring of 5 SDSS double QSOs with the Nordic Optical Telescope

Paraficz, D.; Hjorth, J.; Elíasdóttir, Árdís

doi:10.1051/0004-6361/200811387

Cited by 19 publications

(20 citation statements)

References 40 publications

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“…Image A leads image B by ∆t AB days. Our results coming from four basically very different time-delay estimation techniques are very consistent, and confirm the existing estimation from Paraficz et al (2009), while improving its error bars for the spline fit and the NMF techniques used on the complete data set. That the error bars for the dispersion technique, the regression difference, and the spline fit are systematically larger than for the NMF is inherent to the way they are calculated.…”

Section: Fig 2 Results Of the Simultaneous Deconvolution Of 1109 R-bandsupporting

confidence: 82%

“…For SDSS J1206+4332 simultaneous deconvolution reveals the three galaxies that possibly contribute to the lensing potential of the system. We consider the results of the spline fit method as our final best time delay of 111 days and pin down the error bars to 3.5%, thus improving the uncertainty over a previously published result (Paraficz et al 2009). …”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Eulaers

Tewes

Magain

et al. 2013

A&A

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Aims. Within the framework of the COSMOGRAIL collaboration we present 7-and 8.5-year-long light curves and time-delay estimates for two gravitationally lensed quasars: SDSS J1206+4332 and HS 2209+1914. Methods. We monitored these doubly lensed quasars in the R-band using four telescopes: the Mercator, Maidanak, Himalayan Chandra, and Euler telescopes, together spanning a period of 7 to 8.5 observing seasons from mid-2004 to mid-2011. The photometry of the quasar images was obtained through simultaneous deconvolution of these data. The time delays were determined from these resulting light curves using four very different techniques: a dispersion method, a spline fit, a regression difference technique, and a numerical model fit. This minimizes the bias that might be introduced by the use of a single method. Results. The time delay for SDSS J1206+4332 is ∆t AB = 111.3 ± 3 days with A leading B, confirming a previously published result within the error bars. For HS 2209+1914 we present a new time delay of ∆t BA = 20.0 ± 5 days with B leading A. Conclusions. The combination of data from up to four telescopes have led to well-sampled and nearly 9-season-long light curves, which were necessary to obtain these results, especially for the compact doubly lensed quasar HS 2209+1914.

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Section: Fig 2 Results Of the Simultaneous Deconvolution Of 1109 R-bandsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Eulaers

Tewes

Magain

et al. 2013

A&A

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“…In §4.1 we found H 0 = 85 +14 −13 km s −1 Mpc −1 (68% CL) on the basis of lensing alone. This result is higher than, but still consistent with, measurements from other recent lensing (e.g., Jakobsson et al 2005;Paraficz et al 2009;Oguri 2007) and non-lensing (e.g., Freedman et al 2001;Riess et al 2009;Dunkley et al 2008;Komatsu et al 2008) studies. In spite of the extensive lensing data we have obtained, the uncertainty in H 0 from Q0957 is still larger than from most other lenses (see Fig.…”

Section: Hubble Constantsupporting

confidence: 91%

Improved Constraints on the Gravitational Lens Q0957+561. Ii. Strong Lensing

Nakajima

Bernstein

Fadely

et al. 2010

ApJ

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We present a detailed strong lensing analysis of an HST/ACS legacy dataset for the first gravitational lens, Q0957+561. With deep imaging we identify 24 new strongly lensed features, which we use to constrain mass models. We model the stellar component of the lens galaxy using the observed luminosity distribution, and the dark matter halo using several different density profiles. We draw on the weak lensing analysis by Nakajima et al. (2009) to constrain the mass sheet and environmental terms in the lens potential. Adopting the wellmeasured time delay, we find H 0 = 85 +14 −13 km s −1 Mpc −1 (68% CL) using lensing constraints alone. The principal uncertainties in H 0 are tied to the stellar mass-to-light ratio (a variant of the radial profile degeneracy in lens models). Adding constraints from stellar population synthesis models, we obtain H 0 = 79.3 +6.7 −8.5 km s −1 Mpc −1 (68% CL). We infer that the lens galaxy has a rising rotation curve and a dark matter distribution with an inner core. Intriguingly, we find the quasar flux ratios predicted by our models to be inconsistent with existing radio measurements, suggesting the presence of substructure in the lens. arXiv:0909.1807v2 [astro-ph.CO]

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“…For a double image system, model assumptions must be made (e.g. Paraficz et al 2009), or high resolution imaging of the quasar host galaxy must be obtained (Suyu 2012). However, focusing on quads has the potential to bias the inference on cosmological parameters, if these systems are a biased subset of the lens population.…”

Section: Introductionmentioning

confidence: 99%

Observational selection biases in time-delay strong lensing and their impact on cosmography

Collett

Cunnington

2016

Mon. Not. R. Astron. Soc.

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Inferring cosmological parameters from time-delay strong lenses requires a significant investment of telescope time; it is therefore tempting to focus on the systems with the brightest sources, the highest image multiplicities and the widest image separations. We investigate if this selection bias can influence the properties of the lenses studied and the cosmological parameters that are inferred. Using a population of lenses with ellipsoidal powerlaw density profiles, we build a sample of double and quadruple image systems. Assuming reasonable thresholds on image separation and flux, based on current lens monitoring campaigns, we find that the typical density profile slopes of monitorable lenses are significantly shallower than the input ensemble. From a sample of quadruple image lenses we find that this selection function can introduce a 3.5% bias on the inferred time-delay distances if the ensemble of deflector properties is used as a prior for a cosmographical analysis. This bias remains at the 2.4% level when high resolution imaging of the quasar host is used to precisely infer the density profiles of individual lenses. We also investigate if the lines-of-sight for monitorable strong lenses are biased. After adding external convergence, κ, and shear to our lens population we find that the expectation value for κ is increased by 0.004 and 0.009 for doubles and quads respectively. κ is degenerate with the value of H 0 inferred from time delays; fortunately the shift in κ only induces a 0.9 (0.4) percent bias on H 0 for quads (doubles). We therefore conclude that whilst the properties of typical quasar lenses and their lines-of-sight do deviate from the global population, the total magnitude of this effect is likely a subdominant effect for current analyses, but has the potential to be a major systematic for samples of ∼25 or more lenses.

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Results of optical monitoring of 5 SDSS double QSOs with the Nordic Optical Telescope

Cited by 19 publications

References 40 publications

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Improved Constraints on the Gravitational Lens Q0957+561. Ii. Strong Lensing

Observational selection biases in time-delay strong lensing and their impact on cosmography

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