STRONG LENS TIME DELAY CHALLENGE. I. EXPERIMENTAL DESIGN

Abstract

The time delays between point-like images in gravitational lens systems can\nbe used to measure cosmological parameters. The number of lenses with measured\ntime delays is growing rapidly; the upcoming \\emph{Large Synoptic Survey\nTelescope} (LSST) will monitor $\\sim10^3$ strongly lensed quasars. In an effort\nto assess the present capabilities of the community to accurately measure the\ntime delays, and to provide input to dedicated monitoring campaigns and future\nLSST cosmology feasibility studies, we have invited the community to take part\nin a "Time Delay Challenge" (TDC). The challenge is organized as a set of\n"ladders," each containing a group of simulated datasets to be analyzed blindly\nby participating teams. Each rung on a ladder consists of a set of realistic\nmock observed lensed quasar light curves, with the rungs' datasets increasing\nin complexity and realism. The initial challenge described here has two\nladders, TDC0 and TDC1. TDC0 has a small number of datasets, and is designed to\nbe used as a practice set by the participating teams. The (non-mandatory)\ndeadline for completion of TDC0 was the TDC1 launch date, December 1, 2013. The\nTDC1 deadline was July 1 2014. Here we give an overview of the challenge, we\nintroduce a set of metrics that will be used to quantify the goodness-of-fit,\nefficiency, precision, and accuracy of the algorithms, and we present the\nresults of TDC0. Thirteen teams participated in TDC0 using 47 different\nmethods. Seven of those teams qualified for TDC1, which is described in the\ncompanion paper II.\n