Time delay for the gravitational lens system B0218+357

Abstract

Measurement of the time delay between multiple images of a gravitational lens system is potentially an accurate method of determining the Hubble constant over cosmological distances. One of the most promising candidates for an application of this technique is the system B0218+357 which was found in the Jodrell Bank/VLA Astrometric Survey (JVAS). This system consists of two images of a compact radio source, separated by 335 milliarcsec, and an Einstein ring which can provide a strong constraint on the mass distribution in the lens. We present here the results of a three-month VLA monitoring campaign at two frequencies. The data are of high quality and both images show clear variations in total flux density, percentage polarization and polarization position angle at both frequencies. The time delay between the variations in the two images has been calculated using a chi-squared minimization to be 10.5 ± 0.4 days at 95 per cent confidence, with the error being derived from Monte-Carlo simulations of the light curves. Although mass modelling of the system is at a preliminary stage, taking the lensing galaxy to be a singular isothermal ellipsoid and using the new value for the time delay gives a value for the Hubble constant of 69 +13 −19 km s −1 Mpc −1 , again at 95 per cent confidence.

Unevenly-sampled signals: a general formalism for the Lomb-Scargle periodogram

“…Figure 10 shows an experimental (mean-subtracted) time series versus its rebinned version. This time series, which is characterized by rather irregular sampling, was obtained with the VLA array (Biggs et al 1999) and consists of polarisation position angle measurements at an observing frequency of 15 GHz for one of the images of the double gravitational lens system B0218+357. The original sequence contains only M = 45 data and it is rebinned on a regular grid of M r = 92 time instants.…”

VLBI phase-reference observations of the gravitational lens JVAS B0218+357

“…The background source has properties of a powerful radio source and a red optical continuum (Stickel & Kuhr 1993), based on which it is conjectured to be a blazar, and its redshift has been confirmed using optical spectroscopy (z = 0.944, Cohen et al 2003;Browne et al 1993). Further, it is variable in its radio emission and an accurate value for the time delay between variations in the images has been measured by Biggs et al (1999), (10.5 ± 0.4) days (see also Cohen et al 2000). (Patnaik et al, unpublished).…”

“…c O'Dea et al (1992). d Biggs et al (1999) (The flux-densities are averaged over the time-period of the observations, and the ratio is corrected for flux variability and the time delay; see text).…”

Intrinsic Intraday Variability in the Gravitational Lens System B0218+357

“…If an IDV source is multiply imaged, only intrinsic variations should be correlated in the images. We have recently measured a time delay of 10.5 ± 0.4 d in the lensed system B0218+357, exploiting its rapid radio variability (Biggs et al 1999). We show the VLA 15-GHz light curves in Fig.…”