Emission pattern for different models. The radial axis is the observed efficiency, given by η_obs ≡ f(θ, a)η(a), i.e., the observed luminosity normalized on Ṁc² (the accretion rate is the same for each model). Left panel: classical nonrelativistic SS model (dashed blue line) compared with a = −1 (orange line), a = 0 (green line) and a = 0.797 (red line) KERRBB patterns. For the SS model (η_SS ~ 0.083), the observedefficiency is η_obs = 2cosθη_SS ≈ 0.17cosθ. The a = 0.797 case describes the most similar KERRBB model to a SS with the same parameters (mass and accretion rate) at θ = 0^°. At different viewing angles, the KERRBB model is brighter. For the SS model, the emission has a circular pattern while for KERRBB, the pattern is “warped” by the relativistic effects. Right panel: SS model (dashed blue line) compared with a = −1 (green line), a = 0.95 (orange line) and a = 0.9982 (red line) KERRBB patterns. For the extreme KERRBB, the emission is strongly modified with respect to the others and the observed disk luminosity is larger for larger angles. Red dots indicate the angle at which the KERRBB observed disk luminosity is maximized, obtained through Eq. (11): for a ≲ 0.8, θ_max ~ 2^°; for a = 0.95, θ_max ~ 25^°; for a = 0.9982, θ_max ~ 64^° (see Table 1 for other spin values).