X-shaped radio sources as parent population of core-dominated triple
  blazars
  There are a number of theories explaining the nature of the so-called
X-shaped radio sources. According to one of them, an X-shaped source is indeed
a cross whose one arm is associated with a double radio source that has changed
its orientation in space, while the other arm is associated with relic lobes
and its position indicates the former direction of the jets. Here, I present
two new arguments in favour of this conjecture. Firstly, it is obvious that
shortly after the repositioning, the pair of the new lobes must be very
compact. To illustrate such a possibility, I show an EVN image of the central
component of a triple source J1625+2712. When resolved, it appears as a compact
double that is not aligned with the outer double so the whole source is indeed
X-shaped. Secondly, I consider the situation when one of the arms of an
X-shaped source is not intrinsically short but foreshortened by projection. I
show two examples of triple sources whose central component is a blazar and the
span of the lobes that straddle it amounts to more than 6\times10^5 pc. An
assumption that sources of this kind have one axis, and so the lobes are beamed
in the same way the core is, would require unrealistically huge deprojected
linear sizes. Therefore, I claim that core-dominated triples (CDT) like these
two have two axes: the one pertinent to the relic lobes is not pointed towards
us so they are not beamed/foreshortened, whereas the axis pertinent to the jets
makes a small angle with the line of sight so that a blazar is observed. It
follows that X-shaped sources must be actual crosses and they are the parent
(unbeamed) population of at least some CDT blazars, particularly those with
large overall sizes.
