A Determination ofH₀with the CLASS Gravitational Lens B1608+656. III. A Significant Improvement in the Precision of the Time Delay Measurements

Abstract

The gravitational lens CLASS B1608+656 is the only four-image lens system for which all three independent time delays have been measured. This makes the system an excellent candidate for a high-quality determination of H 0 at cosmological distances. However, the original measurements of the time delays had large (12-20%) uncertainties, due to the low level of variability of the background source during the monitoring campaign. In this paper, we present results from two additional VLA monitoring campaigns. In contrast to the ∼5% variations seen during the first season of monitoring, the source flux density changed by 25-30% in each of the subsequent two seasons. We analyzed the combined data set from all three seasons of monitoring to improve significantly the precision of the time delay measurements; the delays are consistent with those found in the original measurements, but the uncertainties have decreased by factors of two to three. We combined the delays with revised isothermal mass models to derive a measurement of H 0 . Depending on the positions of the galaxy centroids, which vary by up to 0. ′′ 1

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.…”

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

“…Owing to the accuracies on the time delays of a few percents currently achieved for quads (e.g. Fassnacht et al 2002;Courbin et al 2011;Tewes et al 2013), time delay measurements in quadruply lensed systems could in the most favourable cases break the SPT independently of H 0 .…”

Two Accurate Time-Delay Distances From Strong Lensing: Implications for Cosmology

“…Accurate, long duration, and well-sampled light curves are necessary to obtain accurate time delays in the presence of microlensing. Modern light curves have much higher photometric precision, sampling, and duration (Fassnacht et al 2002;Courbin et al 2011) compared to the early pioneering light curves (e.g., Lehar et al 1992). High-resolution images of extended features in the source, and stellar kinematics of the main deflector, provide hundreds to thousands of data points to constrain the mass model of the main deflector, thus reducing the degeneracy between the distance and the gravitational potential of the lens that affected previous models constrained only by the positions of the lensed quasars (e.g., Schechter et al 1997).…”