COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Abstract

We present accurate time delays for the quadruply imaged quasar HE 0435-1223. The delays were measured from 575 independent photometric points obtained in the R-band between January 2004 and March 2010. With seven years of data, we clearly show that quasar image A is affected by strong microlensing variations and that the time delays are best expressed relative to quasar image B. We measured Δt BC = 7.8 ± 0.8 days, Δt BD = −6.5 ± 0.7 days and Δt CD = −14.3 ± 0.8 days. We spacially deconvolved HST NICMOS2 F160W images to derive accurate astrometry of the quasar images and to infer the light profile of the lensing galaxy. We combined these images with a stellar population fitting of a deep VLT spectrum of the lensing galaxy to estimate the baryonic fraction, f b , in the Einstein radius. We measured f b = 0.65 The spectrum also allowed us to estimate the velocity dispersion of the lensing galaxy, σ ap = 222 ± 34 km s −1 . We used f b and σ ap to constrain an analytical model of the lensing galaxy composed of an Hernquist plus generalized NFW profile. We solved the Jeans equations numerically for the model and explored the parameter space under the additional requirement that the model must predict the correct astrometry for the quasar images. Given the current error bars on f b and σ ap , we did not constrain H 0 yet with high accuracy, i.e., we found a broad range of models with χ 2 < 1. However, narrowing this range is possible, provided a better velocity dispersion measurement becomes available. In addition, increasing the depth of the current HST imaging data of HE 0435-1223 will allow us to combine our constraints with lens reconstruction techniques that make use of the full Einstein ring that is visible in this object. Key words. cosmological parameters -gravitational lensing: strong Based on observations made with the 1.2 m Euler Swiss Telescope, the 1.5 m telescope of Maidanak Observatory in Uzbekistan, and with the 1.2 m Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los

Planck2013 results. XVI. Cosmological parameters

“…1, after the submission of this paper Humphreys et al (2013) Reid et al 2013, for a detailed analysis of UGC 3789). The point labelled "RXJ1131-1231" shows the estimate H 0 = 78.7 +4.3 −4.5 km s −1 Mpc −1 derived from gravitational lensing time delay measurements of the system RXJ1131-1231, observed as part of the "COSmological MOnitoring of GRAvitational Lenses" (COSMOGRAIL) project (Suyu et al 2013, see also Courbin et al 2011;Tewes et al 2013). Finally, the point labelled SZ clusters shows the value H 0 = 76.9 +10.7 −8.7 km s −1 Mpc −1 (Bonamente et al 2006), derived by combining tSZ and X-ray measurements of rich clusters of galaxies (see Carlstrom et al 2002, and references therein).…”

Sn Refsdal: Photometry and Time Delay Measurements of the First Einstein Cross Supernova

“…In recent years, high precision time delays have been measured for a growing sample of multiply-imaged quasars, using increasingly sophisticated observations and techniques (e.g., Fassnacht et al 2002;Kochanek 2006;Courbin et al 2011;Eulaers et al 2013;Tewes et al 2013b) Measuring time delays from lensed SNe like SN Refsdal should in principle be much simpler than is typically the case for lensed quasars. The time variation of quasars is stochastic, being driven by essentially random events on the accretion disk of the central supermassive black hole, so the intrinsic shape of a quasar light curve can not be known a priori.…”

“…The SN Refsdal light curve is not as finely sampled or covering as long a baseline as is now typical for multiplyimaged quasars, which in some cases are monitored over 5-10 years (e.g., Courbin et al 2011;Eulaers et al 2013;Tewes et al 2013b). However, a microlensing analysis of SN Refsdal would have several distinct advantages relative to the quasar observations.…”

Tailoring strong lensing cosmographic observations

“…Due to their repeat observations, they can also monitor the image fluxes over several years to measure the time delay ∆t. This may be supplemented with further cadenced observations from external programs, along the lines of the highly successful COSMOGRAIL program [23].…”