Lens Model and Time Delay Predictions for the Sextuply Lensed Quasar SDSS J2222+2745

TL;DR

This study refines the lens model of the sextuply lensed quasar SDSS J2222+2745 using new imaging, spectroscopy, and X-ray data, accurately predicting time delays and magnifications to improve understanding of the lensing system.

Contribution

The paper provides a detailed lens model incorporating new spectroscopic redshifts and X-ray data, and predicts time delays for the first time in this system.

Findings

Model agrees with recent time delay measurements

Predicted time delays for faint quasar images are provided

X-ray emission detected from both the quasar and the cluster

Abstract

SDSS J2222+2745 is a galaxy cluster at z=0.49, strongly lensing a quasar at z=2.805 into six widely separated images. In recent HST imaging of the field, we identify additional multiply lensed galaxies, and confirm the sixth quasar image that was identified by Dahle et al. (2013). We used the Gemini North telescope to measure a spectroscopic redshift of z=4.56 of one of the secondary lensed galaxies. These data are used to refine the lens model of SDSS J2222+2745, compute the time delay and magnifications of the lensed quasar images, and reconstruct the source image of the quasar host and a second lensed galaxy at z=2.3. This second galaxy also appears in absorption in our Gemini spectra of the lensed quasar, at a projected distance of 34 kpc. Our model is in agreement with the recent time delay measurements of Dahle et al. (2015), who found tAB=47.7+/-6.0 days and tAC=-722+/-24 days. We use the observed time delays to further constrain the model, and find that the model-predicted time delays of the three faint images of the quasar are tAD=502+/-68 days, tAE=611+/-75 days, and tAF=415+/-72 days. We have initiated a follow-up campaign to measure these time delays with Gemini North. Finally, we present initial results from an X-ray monitoring program with Swift, indicating the presence of hard X-ray emission from the lensed quasar, as well as extended X-ray emission from the cluster itself, which is consistent with the lensing mass measurement and the cluster velocity dispersion.