Observed SBO properties, including the observed SBO luminosity L_SBO (top), peak timescale t_SBO (middle), and color temperature T_col,SBO (bottom), in the r_out−M_CSM plane. The colored region indicates the parameter space where an RMS can be formed and produce an observable SBO, while the gray region corresponds to cases where SBO cannot occur. In the top and middle panels, the dashed line separates the light-travel-dominated regime (t_diff < t_lt; left) from the photon-diffusion-dominated regime (t_diff > t_lt; right) for the observed luminosity and duration. In the bottom panel, the dashed line separates the LTE SBO regime (η ≤ 1; above) from the non-LTE regime (η > 1; below). Here, χ = 0.1, M_ej = 2 M_⊙, and E_kin = 10⁵¹ erg are fixed.