What are Targets of Opportunity (ToOs)?

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Targets of Opportunity (ToO) are transient phenomena whose exact timing and/or location on the sky are uncertain at the time of the proposal submission. They include objects that can be generically identified before the onset of such phenomena (e.g., recurrent novae, variable stars) and objects that cannot a priori be specifically identified (e.g., newly discovered comets, novae, supernovae, gamma-ray bursts). Requests for observations of these objects should be submitted through the normal General Observer proposal process in response to a Call for Proposals. Observations of completely unanticipated phenomena can be requested through Director's Discretionary Time procedures.

Classifications of Impact

Targets of Opportunity are categorized by the extent to which the execution of such an observation affects normal Spitzer scheduling and observing procedures. As part of the proposal submission, GO investigators should self-classify each ToO request, based upon the maximum delay -- in their judgment -- that is scientifically acceptable between the activation of an approved AOR and the execution of the observation:

High-Impact	< 1 week (normally a minimum 48-hour turnaround)
Medium-Impact	1-5 weeks
Low-Impact	> 5 weeks.

In the Warm Mission high and medium impact ToO observations can only be submitted via Director's Discretionary Time.

Apart from the overhead burdens applied to all Spitzer observations, the SSC will impose no additional overheads on low-impact ToO observations. The SSC has developed separate calculations of Observatory overheads to be assessed against the high- and medium-impact categories of ToO observations. Current estimates of these special overhead burdens are included as part of Spot (click on the "Special" button in any AOT window) and are subject to change in future CPs.

In general, the more disruptive the ToO observation is to normal Spitzer scheduling and operations, the stronger the scientific justification must be to approve the proposed observation. (See How Scheduling Works for more information.)

In the warm mission, only IRAC is used so multiple instrument overheads should not be used.

Activation of AORs

A General Observer proposal must include a valid Astronomical Observation Request (AOR) for each predictable ToO observation. The AOR must be completed in as much detail as possible, lacking perhaps the precise target position (i.e., a null target) and refined integration times. The proposal must present a detailed plan of observations that will be implemented if the specific event occurs. Moreover, it must also provide an estimate of the probability of occurrence of the specified event during the relevant Spitzer observing cycle(s).

After a ToO proposal is approved, a request for AOR activation must be electronically submitted to the SSC Director by the Principal Investigator (PI) via the SSC Helpdesk (help@spitzer.caltech.edu). Following the request for activation, the SSC will ascertain the feasibility of conducting the ToO observations, taking into account sky visibility and the schedule of Spitzer instrument campaigns. The observer will also submit a revised AOR, with precise coordinates and integration time. If the observations cannot be conducted on a schedule requested by the investigator, the SSC Director will consult with the PI on the scientific utility of later observations. The SSC Director must issue final approval for any high-impact ToO observations requiring an interruption of the onboard observing schedule.

An approved ToO observation will be executed only in the event that the specified phenomenon actually occurs within the relevant observing cycle. If the triggering event for an approved ToO observation does not occur during the observing cycle, the AOR will be deactivated at the end of the cycle. In the event that a ToO observation expires without execution, the allotted observing time will be returned to the General Observer pool.

Regulation of Observations

The SSC Director will rely on the recommendations of the Time Allocation Committee to assess the benefits of a proposed ToO observation against any disruptions to the efficient planning and scheduling of science observations with Spitzer. Because of the heavy impact that high-impact ToO observations will have on the short- and medium-term Spitzer schedule, medium- and high-impact ToO observations must be submitted via Director's Discretionary Time. Only low-impact ToOs are permitted in response to General Observer Calls for Proposals. In Cycle-6 we anticipate being able to support only 1-2 medium/high impact ToOs.

Data Rights and Analysis Funding

As a type of General Observer program, data rights and funding policies for ToO observations are the same as for GOs.

The SSC Director reserves the right to request early release of ToO data by the Principal Investigator when such a release is deemed to be of interest to the general public, as determined by the Director.

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