Signatures of restarted activity in core-dominated, triple radio sources selected from the FIRST survey

Signatures of re-occurrence of activity in radio-loud AGNs, indicated either by the so-called double-double or X-shaped structures, have been observed in a number of radio sources. All such objects known to date have linear sizes of the order of a megaparsec. A number of sources which are appreciably more compact than this, but which exhibit hints of a past phase of activity, have been found in the VLA FIRST survey. Their structures show symmetric relic lobes straddling relatively bright, unresolved cores. The cores of 15 of these have been observed with MERLIN at 5 GHz, which has shown that four of them are doubles or core-jets on the subarcsecond scale. Misalignments \Delta PA > 30 degrees between the axis of the inner structure and the line connecting the fitted maxima of the arcminute-scale relic lobes are clearly visible in three of the four sources. It can be readily inferred from these results that a rapid repositioning of the central engine in each of these three radio sources is the most plausible interpretation of the observed morphology and that a merger is the most likely the original cause of such a repositioning. In the case of TXS 1033+026, the optical image extracted from the SDSS archives clearly suggests that two objects separated by only 2.7 kpc (projected onto the sky plane) are indeed merging. The inner parts of TXS 0818+214 and TXS 1312+563 could be interpreted as double-lobed and consequently, these sources could be of the double-double type, but further multifrequency observations are necessary to provide support for such an interpretation