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Variability is a general property of accretion discs and their associatedjets. We introduce a semi-analytic model for particle acceleration and radiojet/lobe evolution and explore the effect of Myr timescale jet variability onthe particles accelerated by an AGN jet. Our work is motivated by the need forlocal powerful ultrahigh energy cosmic ray (UHECR) sources and evidence forvariability in AGN and radio galaxies. Our main results are: i) UHECR andnonthermal radiative luminosities track the jet power but with a response setby the escape and cooling times, respectively; ii) jet variability producesstructure in the electron, synchrotron and UHECR spectra that deviates fromthat produced for a constant jet power - in particular, spectral hardeningfeatures may be signatures of variability; iii) the cutoff in the integrated CRspectrum is stretched out due to the variation in jet power (and, consequently,maximum CR energy). The resulting spectrum is the convolution of the jet powerdistribution and the source term. We derive an approximate form for alog-normal distribution of powers; iv) we introduce the idea of $\sim 10$ GeV'proxy electrons' that are cooling at the same rate that UHECRs of rigidity 10EV are escaping from the source, and determine the corresponding photonfrequencies that probe escaping UHECRs. Our results demonstrate the linkbetween the history of an astrophysical particle accelerator and its particlecontents, nonthermal emission and UHECR spectrum, with consequences forobservations of radio galaxies and UHECR source models.

Particle acceleration in radio galaxies with flickering jets: GeV electrons to ultrahigh energy cosmic rays