Kurtosis as a function of the time lag τ rescaled to the proton cyclotron resonance timescale t_res = 1/f_res = 2π(V_A + v_th)/(Ω_cV_sw) in lin-log axis. It is important to notice that the minimum timescale at which the kurtosis has been plotted corresponds to the highest frequency shown in the PSD in Fig. 4a. Smaller timescales indeed are highly affected by instrumental noise. Error bars are also displayed (see text for further details). The horizontal dashed line indicates the value of the kurtosis for a Gaussian distribution of the magnetic field increments, i.e., K(τ)=3.