COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Abstract

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.

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.…”

A Consistent Picture Emerges: A Compact X-Ray Continuum Emission Region in the Gravitationally Lensed Quasar SDSS J0924+0219

“…Monitoring lenses over time addresses these problems (Kochanek 2004;Kochanek et al 2006;Goicoechea et al 2008) while simultaneously permitting time delay measurements (e.g., recent measurements by Tewes et al 2013;Eulaers et al 2013;Rathna Kumar et al 2013). In particular, the Bayesian Monte Carlo method of Kochanek (2004) enables the extraction of probability densities for the physical parameters of interest (e.g., source size, M , etc.)…”

H0from ten well-measured time delay lenses

“…90.6 ± 1.4 91.7 ± 0.7 ∆t BC −0.7 ± 1.5 −1.4 ± 1.6 ∆t BD 91.4 ± 1.2 92.4 ± 1.4 ∆t CD 91.7 ± 1.5 91.3 ± 1.3 SDSS J1206+4332 (Eulaers et al 2013) R ∆t AB 111.3 ± 3 110.3 ± 1.9 H1413+117 (Goicoechea & Shalyapin 2010) r ∆t AB −17 ± 3 −14.3 ± 5.5 ∆t AC −20 ± 4 −19.9 ± 10.9 ∆t AD 23 ± 4 24.0 ± 6.8 ∆t BC ? ∆t BD ?…”