Original version
The Astrophysical Journal (ApJ). 2023, 955 (2):140, DOI: https://doi.org/10.3847/1538-4357/acee7e
Abstract
The gravitational lens system PS J0147+4630 (Andromeda’s Parachute) consists of four quasar images ABCD and a lensing galaxy. We obtained r -band light curves of ABCD in the 2017−2022 period from monitoring with two 2 m class telescopes. Applying state-of-the-art curve-shifting algorithms to these light curves led to measurements of time delays between images, and the three independent delays relative to image D are accurate enough to be used in cosmological studies (uncertainty of about 4%): Δ t AD = −170.5 ± 7.0, Δ t BD = −170.4 ± 6.0, and Δ t CD = −177.0 ± 6.5 days, where image D is trailing all the other images. Our finely sampled light curves and some additional fluxes in the years 2010−2013 also demonstrated the presence of significant microlensing variations. From the measured delays relative to image D and typical values of the external convergence, recent lens mass models yielded a Hubble constant that is in clear disagreement with currently accepted values around 70 km s −1 Mpc −1 . We discuss how to account for a standard value of the Hubble constant without invoking the presence of an extraordinary high external convergence.