FAQ for Constrained and Coordinated Proposals

What is a time constrained observation?

An observation is time constrained if the proposer restricts the time during which that observation can be performed. This may be because the user has specified that the target can only be observed at certain times, or when an observation cannot be scheduled until triggered (a TOO). Many targets can only be observed at certain times of the year because of pitch angle or sun block restrictions. These observatory-imposed restrictions do not count as "constraints". However, proposers should check that any user-imposed constraints do not push the target into the "cannot do" pitch range (see the Visibility and Constraints Chapter of the Proposers Guide for details)

What makes an observation time constrained?

The following will result in a constrained observation:

• Specifying that an observation be done within specific dates, times or time intervals. This includes window and roll constraints, phase constraints, uninterrupted observations, monitoring and group observations. These are described in the Proposers Observatory Guide
• Any observation that must be coordinated with another space observatory or NRAO.
• Any other constraints not listed above that are specified in the "Remarks" box in the "Constraints" section of RPS.

I want 4 observations of a target, but don't care about the spacing -- days or even months apart is fine. Does this count as time constrained?

Yes!

If you have any scientific requirements for the spacing of observations that are not compelled by target visibility alone, you must mark the observation as constrained. The most efficient way to schedule multiple observations of the same target may be to do them back-to-back. Any requirement that they NOT be scheduled this way would indeed qualify as a constraint. The best way to specify such a constraint on the RPS form is probably with a geometric monitoring series with large tolerance.

How are time constrained observations counted?

Time constrained observations are designated as such in the CXC observation database if any of the RPS fields described above (window, phase, roll etc) are filled out, or if constraints are specified in Remarks. As from Cycle 9, each time constrained observation will be counted as "Easy", "Average" or "Difficult", with annual quotas for each. See the Call for Proposals for details on how constraints are classified and the Counting Constraints Worksheet for real-life examples. Note that the count is done on an observation, not target, basis. Thus a series of 5 monitoring observations of a single source may count as a single target in RPS (only one target form need be filled out) but will count as 5 time constrained observations.

Preferences vs Constraints

It is possible for a proposer to designate a constraint as a "preference". In this scenario the major goals of the project can be achieved without a hard constraint but superior results might be expected if the constraint is met. If an observation is approved by the peer review as "constrained", and is found to be feasible by the CXC, it will be fixed into the appropriate slot in the Long Term Schedule. It will only be moved if there is another slot in the LTS where the constraints can be met. In contrast, a "preference" is met on a best-effort basis.

What is the difference between a Joint Proposal and Coordinated Observations?

A proposal is classified as "joint" if time is requested on one or more observatories (e.g. HST or the VLA) in addition to Chandra. Please see the Call for Proposals for more details. An observation is "coordinated" if the Chandra observations are to be scheduled in conjunction with another space observatory or NRAO. For example, if the observations are required to be simultaneous with, or offset from, those of another observatory. The awarding of joint Chandra time with another observatory does not mean that these observations will necessarily be coordinated.

Please note that with the exception of the VLA, coordination with ground-based observatories is only available as a preference, .

If I apply for joint time, do I also have to check the coordinated box on the RPS forms?

Yes, if the Chandra observation is to be coordinated with another observatory

Many joint projects do not require the observations to occur within the same timeframe. The Chandra mission planners will have no way of knowing that an observation is coordinated if it is not designated as such.

I have observing time on another facility, and they are willing to slave to Chandra's schedule. I will tell them when my Chandra observation is scheduled. Do I need to check the coordinated box?

YES!

If the "coordinated" flag is not set, the observation is unconstrained. Observations that are completely unconstrained are often designated as "pool" targets. Pool targets may be scheduled at any time during the cycle to fill gaps between constrained observations. Therefore they are often scheduled with only a few days notice, making it almost impossible to give the other observatory time to change their schedule.