Target of Opportunity policy at GTC


1. Definition


Targets of Opportunity (ToO) are astronomical objects undergoing unexpected or unpredictable transient phenomena and which are proposed for observation. Because of the transient nature of the event the observations are normally urgent and may require even an immediate intervention at the telescope. ToO include objects that can be identified before the onset of such phenomena (e.g. dwarf novae, X-ray binaries) as well as objects which cannot be identified in advance (e.g. novae, supernovae, gamma-ray bursts). For the former category, target coordinates are specified in the proposal, while for the latter only the target description is required.


2. ToO allocation and override rights


ToO observations can only be requested to and allocated by the respective time allocation committees (TAC). Given the urgency of the observations a ToO observation may require an ongoing programme to be interrupted. Each TAC defines its policy such as maximum duration and allowed frequency of the override, and allocates a specific amount of observing time and allowed observing conditions to the proposal.

When in queue-scheduled observing mode the Observatory will endeavour to carry out the observations as promptly as possible, balancing the urgency and scientific priority of the ToO proposal against the impact on the ongoing observations in the queue. For nights in visitor observing modes each TAC establishes its override policy.

The observations will be carried out respecting the observing conditions approved by the TAC. The PI may propose adapting these observing conditions for specific observing blocks, and the Observatory will endeavor to respect such special requests on a best-efforts basis.


3. Activating a ToO observation


Prior to the trigger of a ToO observation, it is important to check in the GTC´s observing calendar if the current night is devoted to non-scientific activities such as the commissioning of instruments or routinely maintenance of the telescope, as ToO observations would be difficult to be executed in that case.

To make sure that all the information is correctly received and processed in time for the observations override ToO observations for a given night must be activated by e-mail to gtc_too [at] as long as possible in advance of the observation. The relevant information on object position and instrument setup, i.e. the Observing Block information, should be prepared and submitted using the GTC Phase-2 tool on the web. For reasons of efficiency and in order for the observatory to check the validity of Observing Blocks (OBs) prior to the event, the PI must prepare their observing blocks in advance of the observations. Obviously for objects that cannot be identified in advance the coordinates and finding charts will have to be prepared at the last moment before the observations and uploaded into the relevant OB. The instrument setup must be prepared and defined in the OB well in advance in all cases. The current optical elements available in OSIRIS can be found here.

In the case of a very urgent and unanticipated events the PI may contact the GTC support astronomer directly during the night at the telescope, but this should be an exception. In such a case it will normally not be possible for the observatory to make any changes to the instrument setup that requires day time intervention, for instance to interchange optical components.

In order to maintain an efficient queue schedule, the use of two different instruments for a single TOO in the same night should be avoided. In the case of an exceptional need for doing this, user must be aware that the time necessary to reinstate the queue in the same status prior to the trigger will be charged to the observing program.

In the event of a direct conflict between ToO observations, GTC staff will strictly follow the well stablished TAC policy.

Once a request for a ToO observation has been activated, the requested time is subtracted from the time allocated to the program even in case the observation cannot be carried out for any weather or technical reason. When activating a ToO, the PI is advised to indicate the duration of the activation, or to deactivate the ToO, so as to avoid unnecessary observations. The requested and allocated time must include all associated overheads such as target acquisition, night-time calibrations and, in case of override on a visiting observer night, the time necessary to reinstate the original instrumental configuration.


4. Data distribution


The Observatory will disseminate the data through the normal channels, but in preparing the data packages it will give maximum priority to ToO observations. In the case of very urgent observations, scientific data can be also uploaded directly to the GTC FTP server under request.


Last modified: 09 January 2017