Left. WFPC2/F450W black/white image of the 8 o’clock arc showing the positions of the four lensed images of the main galaxy component in red and the blob in blue. The two brightest images labeled A2 and A3 were targeted for spectroscopy with X-shooter. The large ellipse corresponds to the external critical line at the redshift of the arc as derived from lens modeling (Sect. 3.2). Right. WFPC2/F450W-F650W-F814W composite-color image showing the reconstructed morphology of the 8 o’clock arc in the source plane, as derived from the best-fit lens model. The source is formed of two major parts, the main galaxy component (on the left) and a smaller blob (on the right) separated by 0.15 arcsec, or equivalently 1.2 kpc in projected distance. The blob has a twice higher magnification factor than the main galaxy component. In both panels, the horizontal scale bar refers to 1 arcsec.