Gravitational Lens System PS J0147+4630 (Andromeda's Parachute): Main Lensing Galaxy and Optical Variability of the Quasar Images

TL;DR

This study provides detailed spectroscopic and photometric analysis of the gravitational lens system PS J0147+4630, revealing the lens galaxy's properties, quasar image variability, and potential for cosmological measurements.

Contribution

It offers new spectroscopic measurements of the lens galaxy, detects microlensing in quasar images, and estimates time delays, enhancing understanding of this lens system.

Findings

Lens galaxy is an early-type at z=0.678 with 5% velocity dispersion.

Detected microlensing variations of ~0.1 mag in quasar images C and D.

Estimated a few-day delay between quasar images A and B.

Abstract

Because follow-up observations of quadruple gravitational lens systems are of extraordinary importance for astrophysics and cosmology, we present single-epoch optical spectra and $r$--band light curves of PS J0147+4630. This recently discovered system mainly consists of four images ABCD of a background quasar around a foreground galaxy G that acts as a gravitational lens. First, we use long--slit spectroscopic data in the Gemini Observatory Archive and a multi-component fitting to accurately resolve the spectra of A, D, and G. The spectral profile of G resembles that of an early-type galaxy at a redshift of 0.678 $\pm$ 0.001, which is about 20\% higher than the previous estimate. Additionally, the stellar velocity dispersion is measured to $\sim$5\% precision. Second, our early $r$-band monitoring with the Liverpool Telescope leads to accurate light curves of the four quasar images. Adopting time delays predicted by the lens model, the new lens redshift, and a standard cosmology, we report the detection of microlensing variations in C and D as large as $\sim$0.1 mag on timescales of a few hundred days. We also estimate an actual delay between A and B of a few days (B is leading), which demonstrates the big potential of optical monitoring campaigns of PS J0147+4630.