XMM offers the possibility to conduct three special kinds of observations, namely ``linked'', ``pilot/follow-up'' and ``concatenated''.
Concatenated observations are two or more observations that are executed ``back-to-back''.
Based on a first short (``pilot'') observation it is decided, with rapid turn-around, based on a success criterion, whether this will be followed as fast as possible by a longer (``follow-up'') observation of the target, still within the same orbit.
Linked observations are observations consisting of ``test'' observations in one orbit and ``main'' observations in a later orbit which depend on the results obtained from the test observations.