Upper panel: Time-dependent profile of the injected electrons derived from the modelling of the LCs. The portions represented by the solid lines correspond to the injections associated with the observed data. Lower panel: Corresponding PSDs. The step-shaped lines illustrate the ‘raw’ periodogram. The symbols denote the logarithmically binned versions of the PSDs. The thick yellow line shows the pure power-law PSD with an index of −2 (i.e. P(ν′_f)∝ν′_f⁻²).