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The existence of double-double radio galaxies (DDRGs) is evidence forrecurrent jet activity in AGN, as expected from standard accretion models. Adetailed study of these rare sources provides new perspectives forinvestigating the AGN duty cycle, AGN-galaxy feedback, and accretionmechanisms. Large catalogues of radio sources provide statistical informationabout the evolution of the radio-loud AGN population out to high redshifts.Using wide-field imaging with the LOFAR telescope, we study both a well-knownDDRG as well as a large number of radio sources in the field of view. Wepresent a high resolution image of the DDRG B1834+620 obtained at 144 MHz usingLOFAR commissioning data. Our image covers about 100 square degrees andcontains over 1000 sources. The four components of the DDRG B1834+620 have beenresolved for the first time at 144 MHz. Inner lobes were found to point towardsthe direction of the outer lobes, unlike standard FR~II sources. Polarizedemission was detected in the northern outer lobe. The high spatial resolutionallows the identification of a large number of small double-lobed radiosources; roughly 10% of all sources in the field are doubles with a separationsmaller than 1 arcmin. The spectral fit of the four components is consistentwith a scenario in which the outer lobes are still active or the jets recentlyswitched off, while emission of the inner lobes is the result of a mix-up ofnew and old jet activity. From the presence of the newly extended features inthe inner lobes of the DDRG, we can infer that the mechanism responsible fortheir formation is the bow shock that is driven by the newly launched jet. Wefind that the density of the small doubles exceeds the density of FR-II sourceswith similar properties at 1.4 GHz, but this difference becomes smaller for lowflux densities.

Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620: A fresh view on a restarted AGN and doubeltjes