Observations of XMM-Newton which should be performed simultaneously with approved observations at other telescopes require a careful coordination of the planning between two or more science operations centres or observatories. Similarly to ``Fixed-Time'' observations, they reduce the flexibility available to the mission planning for scheduling of observations and often lead to larger than nominal slew overheads.
Observations will be performed simultaneously with other telescopes on a best effort basis. The mission planning will consider requests for simultaneous observations only if the observation was flagged as ``Coordinated'' at the time of proposal submission and approved as such by OTAC.
It is the responsibility of the observer to demonstrate that a target proposed for ``Coordinated Observation'' is visible, i.e. that a common visibility window exists (see Section 5.8.1). It is strongly recommended that targets proposed for coordinated observations have a sufficiently long common visibility window per revolution (i.e. common visibility window observation duration + six hours). ``Coordinated'' observations are approved by OTAC by allocating A or B observing priority.