Δχ² vs. expansion velocity for the two detected lines, individually. The values are calculated assuming the best-fit values in each case, only letting the Gaussian width vary. Because of the higher resolving power of SPI at 1 MeV with respect to lower energies, the value for the expansion velocity derived form the high-energy line (solid black) is more constrained than that from the low-energy line (solid gray). For comparison, the 2σ limits are indicated by the thick dashed line.