We report the discovery of a multiply lensed Ly \alpha 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 \alpha emission in the source galaxy and provide redshifts for more than 21 cluster members , from which we obtain a velocity dispersion of 807 \pm 185 km s ^ { -1 } .
Assuming a singular isothermal sphere profile , the mass within the Einstein ring ( 7.13 \pm 0.38 ^ { \prime \prime } ) 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 .