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Abstract

We want to use HST to decide whether the newly discovered z=6.3 QSO PSOJ083+11 (a) either has the fastest growing supermassive black hole of any high-z QSO, or (b) is the second known gravitationally lensed QSO at z>5. PSOJ083+11 was discovered by us a month ago and follow-up spectroscopy showed remarkable features. Taken at face value, its calibrated black hole mass would only lie around 7x10^7 M_sun, but with the extremely high specific accretion rate L/L_Edd=14. This would be the highest accretion rate of any high-redshift QSO and, if extrapolated back, would only require 100 Myrs of growth to the current mass. If this were a standard early mode of black hole growth, the still lingering "seed problem" of limited time in the early Universe would disappear. However, one very interesting caveat exists: the flux and apparent accretion rate of PSOJ083+11 could be boosted by gravitational lensing. While there is no obvious nearby companion in ground-based images, the ground-based seeing prohibits detecting the vast majority of potential lens configurations. Only HST has the spatial resolution to test for potential lensing in this QSO, and decide whether PSOJ083+11 can subsequently be used for either studying ultra-fast early black hole growth, or, if shown to be lensed, be a prime source for studies of the IGM and the QSO host galaxy through its spatial and flux magnification. We want to test the lensing hypothesis by both searching for multiple QSO images in WFC3/IR J-band images, as well as directly search for an intervening galaxy with an ACS narrow band in the QSOs Gunn-Peterson absorption trough, where the QSO light is minimal.