Targets of Opportunity (TOOs) are astronomical events observable by XMM-Newton,
which cannot be predicted and scheduled on the time scale of a year, yet are
scientifically sufficiently important to justify interrupting the
overall XMM-Newton program.
Because these events often need rapid reaction times, the overall
responsibility lies with the Project Scientist, who may coordinate
his decision with a chairperson of the OTAC.
The Project Scientist or his deputy, makes the decision for an
interruption of the program.
The XMM-Newton project recognizes two kinds of TOOs: pre-planned
TOOs and unanticipated TOOs.