A highly magnified supernova at z=1.703 behind the massive galaxy   cluster Abell 1689
  Our ability to study the most remote supernova explosions, crucial for the understanding of the evolution of the high-redshift universe and its expansion rate, is limited by the light collection capabilities of telescopes. However, nature offers unique opportunities to look beyond the range within reach of our unaided instruments thanks to the light-focusing power of massive galaxy clusters. Here we report on the discovery of one of the most distant supernovae ever found, at redshift, z=1.703. Due to a lensing magnification factor of 4.3\pm0.3, we are able to measure a lightcurve of the supernova, as well as spectroscopic features of the host galaxy with a precision comparable to what will otherwise only be possible with future generation telescopes. 
R. Amanullah, A. Goobar, B. Cl\'ement, J.-G. Cuby, H. Dahle, T.   Dahl\'en, J. Hjorth, S. Fabbro, J. J\"onsson, J.-P. Kneib,...
astro-ph.CO