HST discovery of a z=3.9 multiply imaged galaxy behind the complex cluster lens WARPS J1415.1+36 at z=1.026

We report the discovery of a multiply lensed Lyα_x000B_ emitter at z=3.90 behind the massive galaxy cluster WARPS J1415.1+3612 at z=1.026. Images taken by the Hubble Space Telescope (HST) using ACS 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 FOCAS on Subaru confirm strong Ly_x000B_ emission in the source galaxy and provide redshifts for more than 21 cluster members, from which we obtain 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.