HST image of the ER at day 7226. The red annulus represents the fitted diffuse ring model, plotted with a width of 2σ. The black points represent the fitted hot spot centroids, while the dashed black ellipse represents the fitted ellipse around the hot spot centroids. Both methods give an estimate of the center of the ER, showcased as a black and red cross mark for the hot spot ellipse and diffuse ring, respectively.