Summary:

The goal of my work was to estimate the Hubble constant $H_0$ through the study of the quadruply lensed, variable QSO SDSSJ1433+6007. I combined multi-filter, archival HST data for lens modelling with a dedicated 3-year long time-delay monitoring campaign using the 2.1 m Fraunhofer telescope at the Wendelstein Observatory.\\
The lens modelling was performed with the public lenstronomy Python package individually for the infrared data, utilizing the higher resolution of the optical data to constrain image positions a priori. This approach revealed two luminous contaminants in one of the near-infrared exposures, which would bias the lensing potentials and cosmological inference if not accounted for. After masking these contaminants, I repeated the modelling and combined the lens posteriors, obtaining a constraint on the Fermat potential with a precision of $\sim 3.3\,\%$.\\
The g'-band Wendelstein light-curve data was reduced and then analyzed using a free-knot spline fitting method implemented in the public Python PyCS3 tools, accounting for microlensing correction. I obtained a precision of $\sim6.6\%$ for the time delays between the QSO images.
By combining the posteriors for the Fermat potential differences and time delays, and assuming a flat $\Lambda$CDM cosmology, I inferred a Hubble constant of $ H_0 = 73.7^{+4.3}_{-3.9}\frac{\text{km}}{\text{s Mpc}}$ achieving $\sim 6\,\%$ uncertainty for this single system.

For more information please contact Teixeira E.