Velocity dispersion profile of M 15 stars. The upper panel shows the V_r distribution as a function of distance from the cluster centre for individual stars of the sample. Only stars plotted as dots are retained to compute σ in the various radial bins: crosses are stars rejected only because they are local 3σ outliers of the bins. The mean V_r − ⟨ V_sys ⟩ is marked by the continuous horizontal line. Comparison of the observed velocity dispersion profile of M 15 with the King model with a core radius r_C = 0.07′and a concentration C = 2.5, from Trager et al. (1993) and normalised to σ₀ = 13.2 km s^-1 (continuous line; our estimate) and σ₀ = 14.5 km s^-1 (dotted line; by McNamara et al. 2003). The large filled pentagons are the dispersions estimated in the corresponding bins displayed in the upper panel, with their bootstrapped errors. The number of stars per bin is also reported above the points. The open pentagon is the value of σ at the centre of M 15 from McNamara et al. (2003).