16444

In August 2020 we obtained spectroscopic confirmation of a gravitationally lensed arc at z=3.29 which is exceptionally bright. At its redshift comma or higher comma it is the brightest arc known. The galaxy cluster responsible for the lensing is also extraordinarydoublePoint The cluster redshift is z=1.5 and the arc is seen at a large angular radius of 18d_comma comma more extreme than any previously known cluster lens at these redshifts. The bright lensed source with a spectroscopically measured redshift provides a unique opportunity to use strong lensing to accurately constrain a cluster mass distribution at an early epoch where such measurements have previously not been possible. Through a modest investment of 3 HST orbits comma this programme will both produce significant results on its own and be timely preparation for future observations of an extraordinary lensed source and lensing cluster in the coming JWST era.