Time Delay Lens Modeling Challenge: I. Experimental Design
  Strong gravitational lenses with measured time delay are a powerful tool to
measure cosmological parameters, especially the Hubble constant ($H_0$). Recent
studies show that by combining just three multiply-imaged AGN systems, one can
determine $H_0$ to 2.4% precision. Furthermore, the number of time-delay lens
systems is growing rapidly, enabling the determination of $H_0$ to 1% precision
in the near future. However, as the precision increases it is important to
ensure that systematic errors and biases remain subdominant. For this purpose,
challenges with simulated datasets are a key component in this process.
Following the experience of the past challenge on time delay, where it was
shown that time delays can indeed be measured precisely and accurately at the
sub-percent level, we now present the "Time Delay Lens Modeling Challenge"
(TDLMC). The goal of this challenge is to assess the present capabilities of
lens modeling codes and assumptions and test the level of accuracy of inferred
cosmological parameters given realistic mock datasets. We invite scientists to
model a set of simulated HST observations of 50 mock lens systems. The systems
are organized in rungs, with the complexity and realism increasing going up the
ladder. The goal of the challenge is to infer $H_0$ for each rung, given the
HST images, the time delay, and stellar velocity dispersion of the deflector
for a fixed background cosmology. The TDLMC challenge starts with the mock data
release on 2018 January 8th. The deadline for blind submission is different for
each rung. The deadline for Rung 0-1 is 2018 September 8; the deadline for Rung
2 is 2019 April 8 and the one for Rung 3 is 2019 September 8. This first paper
gives an overview of the challenge including the data design, and a set of
metrics to quantify the modeling performance and challenge details.
