HUBBLE SPACE TELESCOPE DISCOVERY OF A z = 3 . 9 MULTIPLY IMAGED GALAXY BEHIND THE COMPLEX CLUSTER LENS WARPS J 1415 . 1 + 36 AT z = 1 .

We report the discovery of a multiply lensed Lyα emitter at z = 3.90 behind the massive cluster WARPS J1415.1+3612 at z = 1.026. Images taken by the Hubble Space Telescope using the Advanced Camera for Surveys reveal a complex lensing system that produces a prominent, highly magnified arc and a triplet of smaller arcs grouped tightly around a spectroscopically confirmed cluster member. Spectroscopic observations using the Faint Object Camera and Spectrograph on Subaru confirm strong Lyα emission in the source galaxy and provide the redshifts for more than 21 cluster members with a velocity dispersion of 807 ± 185 km s−1. Assuming a singular isothermal sphere profile, the mass within the Einstein ring (7.13 ± 0. ′′38) corresponds to a central velocity dispersion of 686+15 −19 km s −1 for the cluster, consistent with the value estimated from cluster member redshifts. Our mass profile estimate from combining strong lensing and dynamical analyses is in good agreement with both X-ray and weak lensing results.