Schematic view of Lyα emitter at z = 4.189 amplified by the galaxy cluster A2744 (background color image, F090W, F150W, F200W). The yellow contours mark μ = 50 at z = 4.19 (Bergamini et al. 2023). The NIRSpec MSA pointing (green box) is shown in the bottom left inset, which zooms in on the Lyα arclet and its multiple images, dubbed LAP2-a,b (the cyan lines outline the 3 and 8σ Lyα contour from VLT/MUSE). The upper right inset shows the VLT/MUSE Lyα line emission of LAP2-b. The bottom right inset shows the NIRSpec prism spectrum and error of LAP2-b in F_ν units with the fluxes inferred from the spectrum convolved with NIRCam filters (open squares) and the corresponding measured NIRCam magnitudes indicated.