Program: GN-2016B-Q-28

We propose a 3-year reverberation mapping campaign to measure the size and structure of the broad emission line region and thus the black hole mass in a quasar at redshift 2.82. The quasar is lensed by an intervening galaxy cluster into six images, with three signficantly magnified outer images, for which accurate time delays have now been established in part using Gemini photometry. The faintest of these three images leads the other two outer images - the two most magnified images - by about 2 years, and has brightened by more than a magnitude in the past two years. We thus know that these two trailing images will brighten by more than a magnitude during our campaign. Our ability to predict the future exploiting lensing time delays, and the extraordinary variablity of this quasar, affords a unique opportunity to directly measure a black hole mass at the peak of the quasar era and thus to test and anchor the empirical scaling laws relied upon by studies of black hole growth and demographics over cosmic time.