Time Delay Cosmography: Analysis of Quadruply Lensed QSO SDSSJ1433 from Wendelstein Observatory

Abstract

The goal of this work is to obtain a Hubble constant estimate through the study of the quadruply lensed, variable QSO SDSSJ1433+6007. To achieve this we combine multi-filter, archival $\text{HST}$ data for lens modelling and a dedicated time delay monitoring campaign with the 2.1m Fraunhofer telescope at the $\text{Wendelstein Observatory}$. The lens modelling is carried out with the public $\text{lenstronomy}$ Python package for each of the filters individually. Through this approach, we find that the data in one of the $\text{HST}$ filters (F160W) contain a light contaminant, that would, if remained undetected, have severely biased the lensing potentials and thus our cosmological inference. After rejecting these data we obtain a combined posterior for the Fermat potential differences from the lens modelling in the remaining filters (F475X, F814W, F105W and F140W) with a precision of $\sim 6\%$. The analysis of the $\text{g’}$-band Wendelstein light curve data is carried out with a free-knot spline fitting method implemented in the public Python $\text{PyCS3}$ tools. The precision of the time delays between the QSO images has a range between 7.5 and 9.8$\%$ depending on the brightness of the images and their time delay. We then combine the posteriors for the Fermat potential differences and time delays. Assuming a flat $\hat{I}›$CDM cosmology, we infer a Hubble parameter of $H_0=76.6_{-7.0}^{+7.7}\frac{\mathrm{km}}{\mathrm{Mpc}\mathrm{s}}$, reaching $9.6\%$ uncertainty for a single system.

27 pages, 29 figures, to be submitted to MNRAS