Function χ²(i_o). It stops at large inclination angles because the bulk Lorentz factor becomes greater than 30. Top figure: the ratio M₁/M₂ is M₁/M₂ = 1. When T_p/T_b increases, the minimum decreases and disappears. This means that the function χ²(i_o) does not show a minimum and is a mirage solution. Bottom figure: the ratio M₁/M₂ = 0.37. The function χ²(i_o) has a minimum for T_p/T_b ≈ 8.88 and i_o ≈ 4. The robustness of this solution, defined as the square root of the difference χ²(γ = 30) − χ²(min), is ≈ 1.8 × σ.