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Context. Blazars are a subset of active galactic nuclei (AGN) with jets thatare oriented along our line of sight. Variability and spectral energydistribution (SED) studies are crucial tools for understanding the physicalprocesses responsible for observed AGN emission.  Aims. We report peculiar behaviour in the bright gamma-ray blazar PKS1424-418 and use its strong variability to reveal information about theparticle acceleration and interactions in the jet. Methods. Correlationanalysis of the extensive optical coverage by the ATOM telescope and nearlycontinuous gamma-ray coverage by the Fermi Large Area Telescope is combinedwith broadband, time-dependent modeling of the SED incorporating supplementalinformation from radio and X-ray observations of this blazar.  Results. We analyse in detail four bright phases at optical-GeV energies.These flares of PKS 1424-418 show high correlation between these energy ranges,with the exception of one large optical flare that coincides with relativelylow gamma-ray activity. Although the optical/gamma-ray behaviour of PKS1424-418 shows variety, the multiwavelength modeling indicates that thesedifferences can largely be explained by changes in the flux and energy spectrumof the electrons in the jet that are radiating. We find that for all flares theSED is adequately represented by a leptonic model that includes inverse Comptonemission from external radiation fields with similar parameters.  Conclusions. Detailed studies of individual blazars like PKS 1424-418 duringperiods of enhanced activity in different wavebands are helping us identifyunderlying patterns in the physical parameters in this class of AGN.

Unusual Flaring Activity in the Blazar PKS 1424-418 during 2008-2011