Scientific Impacts of NSF Divestiture on Pulsar Science

Pulsar projects on the GBT can be grouped into five broad categories based upon scheduling needs, and each will be impacted in different ways by a reduction in open skies time. Some of these effects have already been felt under existing reductions in open skies time (e.g., phase connection observations of new pulsars). Further reductions in open skies time will extend these effects to a greater number of projects and increase the frequency with which they arise. The examples below are not exhaustive. If you have a question regarding a particular existing or future pulsar project, contact Ryan Lynch.

The NSF is accepting public comments on proposed changes to the Green Bank Observatory. If you believe that the changes described below will impact you and wyou would like submit a comment, follow the instructions on our website about the Environmental Impact Study. The period for submitting public comment ends on November 19th, 2016.

Projects with Flexible Scheduling

These are projects that do not require observations at specific times or specific cadence, and as such can be scheduled in a fully dynamic fashion. Examples of projects in this category include pulsar searching and surveys, follow-up of new pulsars, transient follow-up, studies of single-pulse or giant pulse behavior, and polarization studies. Some monitoring projects of known pulsars and transients could fall into this category, but this depends on the specific scientific goals. All of these examples assume that specific receivers, rapid response, or coordination with other telescopes are not needed.

These types of projects will be subject to the same constraints as any other project under reduced time for open skies. Increases in oversubscription rate will lead to a much more competitive proposal process, and fewer proposals overall will be accepted and scheduled. Furthermore, projects that require individual sessions longer than 3–6 hours will increasingly difficult to schedule.

Projects Requiring Windowed Scheduling

These are projects that can be flexibly scheduled, but only within certain windows. Examples of projects in this category include many long-term monitoring programs that aim for a specific cadence (e.g. monthly observations) but with some tolerance (e.g., ± one week), and indirectly includes projects that require certain receivers (see below). Again, this assumes that rapid response or coordination with other telescopes are not needed.

These types of projects will become more difficult to schedule because contractual obligations with other partners will limit the size of windows, and other higher priority projects could fill most of the available time within a window.

Projects Requiring Fixed Scheduling

These are projects that must be scheduled at very specific times, or within windows that are very small (e.g. one day), and so cannot at all be scheduled dynamically. Examples of projects in this category include phase connection timing observations of new pulsars (especially binary pulsars that require high cadence to resolve binary orbits), observations at specific binary orbital phases (e.g. Shapiro delay measurements or studies of eclipses), and projects requiring coordination with other telescopes (e.g. multi-wavelength follow-up of pulsars or transients).

We expect that these types of projects will have to be ranked in the top 10% of all proposals to be considered for scheduling. Even then, scheduling will be difficult. Further reduction of open skies time may make it impossible to schedule fixed projects.

Rapid Response and Target of Opportunity Observations

Projects in this category include follow-up of particularly exciting new pulsars and transients. These types of projects will still be considered but will become increasingly difficult to schedule due to contractual obligations with other partners. Certain periods of time may be entirely filled by projects with partners, or such a small amount of time may be available that it becomes impossible to shuffle the schedule to accommodate rapid response and targets of opportunity.

Projects Requiring the Use of Certain Receivers

These types of projects typically require use of either the 342 MHz or 800 MHz prime focus feeds. Examples of these types of projects include certain timing programs that are considered for open skies time, so-called gridding observations of new pulsars detected in 342 MHz surveys, or spectral studies of pulsars and transients.

Only one prime focus feed can be installed at any given time, and switching between feeds requires a GBT maintenance day. Contractual obligations will reduce the number of maintenance days per week that are available for feed changes. Furthermore, some contractual projects require the use of certain feeds, and these will be the primary drivers of availability. This will further complicate scheduling of windowed, fixed, and rapid response projects that require one of the prime focus feeds.

Tips for Mitigating the Impact of Reduced Open Skies Time on Pulsar Science

While it may be impossible to fully mitigate the impacts described above, there are some tips that observers can follow to maximize their chances of being scheduled.

  • Write strong proposals. While this is always good advice, with the proposal process becoming more competitive it will become increasingly important to dot all the i’s and cross all the t’s. Begin preparing proposals early and take special care to justify all requests.
  • Use shorter sessions when possible. By breaking projects into sessions of three hours or less, you make it easier to fit them into the limited time available for open skies.
  • Be as flexible as possible in your requests. Carefully consider your time request and whether or not it is absolutely necessary to achieve your science goals. If possible, request windowed scheduling instead of fixed scheduling, and fully dynamic scheduling instead of windowed scheduling. If fixed or windowed scheduling is absolutely necessary, rigorously justify why this is the case.
  • Limit your reliance on specific receivers. Consider the option of using either prime focus feed, or one of the Gregorian focus receivers (frequencies of 1 GHz and higher) if your science allows.
  • Clearly state your needs in your proposal. This can be done in the science or technical justifications as appropriate. GBO staff and the time allocation committee may not be able to interpret your needs if you do not clearly state them.

As always, questions about pulsar science at the GBT can be directed to Ryan Lynch.