Green Bank Observatory Call for Proposals: 2018A Semester

The Green Bank Observatory (GBO) invites scientists to participate in the GBO’s 2018A Semester Call for Proposals for the Green Bank Telescope (GBT). This page contains the complete proposal call. Proposals requesting the GBT as part of High Sensitivity Array (HSA), and Global 3mm VLBI Array (GMVA) should be submitted through the Long Baseline Observatory’s call (available here).

The submission deadline for Semester 2018A proposals is Tuesday, 1 August 2017, at 17:00 EDT (21:00 UTC).

The GBO wishes to remind proposers of continuing opportunities for joint observations with the Chandra X-ray Observatory, the Hubble Space Telescope, the Swift Gamma-Ray Burst Mission and the Fermi Gamma-ray Space Telescope.

The GBO strongly encourages proposers to carefully read through the “News and Opportunities” section of the proposal below as there have been a number of changes made to instrument availability.

Proposal preparation and submission remain via the NRAO Proposal Submission Tool (PST) available at NRAO Interactive Services. Note that the PST use requires registration. Proposers who need assistance with proposal preparation or have questions regarding the Call or GBT capabilities should contact Observatory staff via the Helpdesk.

News and Opportunities

The 1 August 2017 deadline is for the 2018A Semester observing period on the GBT: 1 February 2018 – 31 July 2018.

Details of all GBT observing modes are in The Proposer’s Guide for the Green Bank Telescope. Proposers should also consult the more general document The Performance of the GBT: A Guide for Planning Observations. Proposers should make sure that they are familiar with the latest versions of these documents before writing their proposal.

Observer Training

Due to reductions in the amount of NSF-supported “open skies” time on the GBT for use by the scientific community, it has become increasingly difficult to train new GBT observers in the way we have traditionally done in the past. As a result, we have introduced observer training schools. It is expected that new GBT observers will attend one of these schools to become qualified to observe on the GBT.  These provide an introduction to general radio astronomical techniques as well as onsite training for new GBT observers.

The next training school will be held September 18-22, 2017 in Green Bank.

We still support new observers who visit the Observatory, where their projects will receive an increased priority for scheduling and where local staff are on hand to assist in the observations.

While at some point observer training schools may be the primary means to certify new GBT observers, we remain committed to providing all the services necessary to ensure that the GBT remains accessible to the entire scientific community, and ask your patience in this time of transition.

Observing Team Members

We would like to remind all project teams of the Green Bank Observatory policy that all observers must be listed as a member of the project team in the GBT Dynamic Scheduling System.

Also, we would like to remind all observers that they should not log into any GBO computing system using another person’s account. Co-Is and students are required to have their own GBO login and account if they are to participate in observing and data reduction.

GBT Instruments

The GBT receivers, backends, and observing modes that are available in Semester 2018A are listed in Tables 1 and 2 below.

Table 1
Receiver Frequency Range
Prime Focus 1 290-395 MHz and 680-920 MHz
L-band 1.15-1.73 GHz
S-band 1.73-2.60 GHz
C-band (linear only – see below) 3.8-8.0 GHz
X-band 8.0-11.6 GHz
Ku-band 12.0-15.4 GHz
K-band Focal Plane Array (7 pixels) 18.0-26.5 GHz
Ka-band 26.0-39.5 GHz
Q-band 38.2-49.8 GHz
W-band 67-93.3 GHz
ARGUS (shared-risk – see below) 80-115.3 GHz, Private PI Instrument, Shared Risk
Mustang2 (shared-risk – see below) 90 GHz, Private PI Instrument, Shared Risk
Table 2
Backend Observing Modes
Versatile Green Bank Astronomical Spectrometer (VEGAS) Continuum (see below), spectral line, pulsar
Digital Continuum Receiver (DCR) Continuum
Mark V Very Long Baseline Array Disk Recorder Very Long Baseline Interferometry
JPL Radar backend Private PI Instrument – Open for Public Use
Breakthrough Listen Private PI Instrument, Shared risk

Session lengths: Proposers should be aware that long scheduling blocks (more than 6 hours) will be very difficult to schedule as a result of the reduced open skies time from the divestment of the GBT by the NSF. Proposers must make clear in the technical justification section how their project can be scheduled in small observing blocks that would more easily fit into the GBT scheduling constraints. This is especially critical for proposals that require fixed or coordinated observing dates, e.g. VLBI observations, pulsar monitoring, radar, etc.

C-band: Proposals wishing to use the GBT C-band receiver should only use linear polarization outputs. The circular polarization of the receiver is currently not preforming correctly and we will not accept any proposals to use the circular polarization output of this receiver.

C-band VLBI on the GBT: The GBO will only accept proposals for VLBI Stokes I continuum observations using the GBT C-band receiver (the observations will need to be done using full Stokes just to calibrate Stoke I). All other VLBI observations requesting the C-band receiver on the GBT will be disregarded. Please see the HSA section of  the Long Baseline Observatory call (available here) for proposals for more details.


Continuum: All modes of VEGAS may now be used for continuum observations. The Proposal Submission Tool has not been updated to reflect this situation. Proposers should use the spectral line modes of VEGAS to choose the desired bandwidth and then note in the technical justification that the observations will be for continuum measurements.

Pulsar: VEGAS pulsar modes will be released for observing.

ARGUS: Observers interested in shared-risk observations using the ARGUS instrument should see the Argus Website for further information. All ARGUS proposals must have permission from the instrument development team.

VLBI: Time available for VLBI on the GBT will be extremely limited as a result of the reduced open skies time from the divestment of the GBT by the NSF. Proposers should only include the GBT in the proposal if it is essential for the science and if it is clearly justified in the text of the proposal. All Very Long Baseline Interferometry (VLBI) proposals requesting the GBT should include any needed setup and overhead time in the time request of their proposals. C-band VLBI observers should see the C-band VLBI note above.

MUSTANG 2: The GBO will accept proposals for shared risk observations using the MUSTANG 2 instrument at the proposal deadline. The GBO cannot guarantee that MUSTANG2 will be cold at the start of scheduled observing due to low observing elevations or rotations of the turret from prior observations. Cool down time for MUSTANG2 observations should be included in the overhead for MUSTANG2 observations. All MUSTANG 2 proposals must have permission from the instrument development team.

Breakthrough Listen backend: The Breakthrough Listen project is making its backend available for up to 50 hours of shared-risk observations during the 2018A semester. The instrument consists of a cluster of 32 Titan X and 1080 GPU-based servers capturing 8-bit baseband voltages over up to 5 GHz of instantaneous bandwidth. Data rates are typically tens of TB/hr but a pipeline is available to generate spectra with adjustable frequency (> 3 GHz) and time (> 350 μs) resolutions, with possible science applications including fast radio transients, pulsar observations, stellar flares, SETI, etc. Before submitting a proposal, proposers must obtain permission from the Breakthrough Listen team at Berkeley SETI Research Center. The team will consult on poroposal preperation and data analysis. Any data acquired using the backend will be proprietary to the proposer per the standard GBO policies.

More information including a technical description of the backend and team contact details can be found here.

Mapping: If you are considering mapping with the GBT such that there are major turns or moves (end of rows in raster map, change in position for pointed maps, etc.) that occur with a cadence faster than every 30 seconds, you will need to consult with a GBT support scientist to ensure that the GBT can safely withstand the stresses induced by the mapping motions.


The GBT is scheduled by the Dynamic Scheduling System (DSS). The DSS system is fully described in the GBT Proposer’s Guide and the GBT Observer’s Guide.

GBT Proposal Preparation

Proposers should consult the The Performance of the GBT: A Guide for Planning Observations and the GBT Observer’s Guide. All proposers, including pulsar proposers, should use the GBT Sensitivity Calculator. Please see the Calculator’s User’s Guide for instructions. The Sensitivity Calculator results can be cut and pasted into the Technical Justification section of the proposal. This will streamline the creation of your Technical Justification and will increase your chances of getting a positive technical review. If you are planning on making maps with the GBT, you should use the GBT Mapping Calculator tool.

The GBT observing policies describe the telescope’s remote observing restrictions.

Proposers requesting GBT participation in High Sensitivity Array (HSA), Very Long Baseline Array (VLBA), or Global Millimeter Very Long Baseline Interferometry (GMVA) observations should consult the VLBA, HSA, and GMVA Proposal Call.

GBT Shared Risk Observing

Observers requesting instruments that are shared-risk may be expected to travel to Green Bank for observations. The observers may be expected to help commission the instruments, to help debug observing and data reduction software, as well as helping to develop data reduction and calibration schemes.

Proposals to use ARGUS (80-115.3 GHz) will be accepted with the instrument development team’s permission. Proposals to use MUSTANG 2 will be accepted with the instrument development team’s permission. Proposals to use the Breakthrough Listen backend will be accepted with the instrument development team’s permission. The Green Bank Observatory will consider shared-risk proposals for observations during the 2018A semester with these instruments.

Limited Time for “Fixed” and “Windowed” Observations

Due to varied pressures on the GBT’s schedule resulting from the reduced open skies time as a result of the divestment of the GBT by the NSF, the amount of time that can be accepted for fixed time observations (e.g. VLBI, pulsar transit observations, etc.) and windowed observations (e.g. monitoring observations) will be limited for the proposal call. Proposals needing fixed and windowed observations will likely have to be ranked at least in or near the top decile in order to be accepted.

Limited Instrument Availability

Due to existing obligations, the Prime Focus 800 MHz feed will only be available for approximately three weeks each month. The Prime Focus 342 MHz feed will only be available for approximately one week per month. The other Prime Focus feeds (450, 600 and Prime Focus 2) are unlikely to be considered for installation. Similarly, the Caltech Continuum Backend (CCB), Zpectrometer, Ku-wide and RRI receiver are also unlikely to be considered for installation. The PFS radar backend (PI: Margot) is available only with prior agreement by the PI.

Table 3
Backend Notes
Prime Focus 1 450 and 600 feed: 385-690 MHz
Prime Focus 2 910-1230 MHz
Caltech Continuum Backend (CCB) Continuum
Zpectrometer 26.0-29.5 GHZ, Private PI Instrument, Shared Risk
Ku-wide 12-18 GHz, not for spectral line use
RRI Private Instrument, Shared Risk
PFS Radar Private PI Instrument

Other GBT Gregorian receivers (primarily, but not limited to, Ku, Ka, Q and W) may only be available during a few short, two or three week periods during the semester.

470-700 MHz RFI: Digital TV transmissions above 470 MHz will make observing very difficult with the 450 and 600 MHz feeds of the PF1 receiver. Available RFI plots do not show the strength of these signals as they overpower the system: they are too low by a factor of 10 to 50. Observers should consult the GBT support scientists before submitting a proposal for these feeds.

RFI at 450 MHz and its harmonics: There is the potential for a major construction project near Green Bank in 2018-2019. For the safety of the workers, a portable radio system at 450 MHz is being proposed for use. Usage would be kept to a minimum. There is the potential for interference at 450 MHz and its harmonics during this time period.

Continuing Opportunities:

Joint Observations with Chandra X-ray Observatory

In previous semesters, the community has had the opportunity to propose for observing time on NRAO facilities through a joint program with the Chandra X-ray Observatory. The Green Bank Observatory will continue with this program and will allocate up to 3% of the open skies time to highly ranked proposals that request time on both HST and the GBT. Proposers to the GBO will have the opportunity to request time on Chandra, to be awarded on the recommendation of the GBO Telescope Allocation Committee (TAC) and approved by the GBO Director. Up to 120 ksec will be made available to GBO/LBO/NRAO proposers annually. See the Joint Observations with Chandra page for details.

Joint Observations with the Hubble Space Telescope (HST)

By agreement between the NRAO (and continued honoring by GBO) and the Space Telescope Science Institute, STScI will be able to award up to 3% of the available open skies time to highly ranked proposals that request time on both HST and the GBT. In return, STScI has offered 30 orbits of HST time for allocation by the GBO/LBO/NRAO TAC to proposals submitted for the GBO deadlines for Semester 2017B and Semester 2018A. See the Joint Observations with HST page for details.

Joint Observations with Swift Gamma-Ray Burst Mission

To foster correlative observations, a joint Swift/NRAO observing program was established, detailed in a Memorandum of Understanding. The GBO will continue to honor this agreement. By this agreement, the Swift Program permits GBO/LBO/NRAO to award up to 300 kiloseconds of Swift observing time per year. Similarly, GBO/LBO/NRAO permits the Swift Guest Investigator (GI) Program to award GBO observing time. See the Joint Observations with Swift page for details.

Joint Observations with Fermi Gamma-ray Space Telescope

We remind the community that it is possible to propose for observing time on the GBT through the Fermi Gamma-ray Space Telescope Joint Proposal Opportunity or the Cooperative Proposal Opportunity. See the Joint Observations with Fermi page for details.

Joint Proposals Between the GBT, LBO, and NRAO

Observing programs that require combinations of the GBT, VLBA, and/or the VLA should submit a proposal for each of the requested telescopes, with a clear justification for each, as has been the case to date. The proposals will be reviewed as before and considered jointly by the Time Allocation Committee. VLBI proposals which request the GBT or VLA (or the HSA, for example) as elements of the VLBI array do not need separate proposals – those telescopes can be selected as separate VLBI stations from a VLBA/HSA proposal.

Other Proposal Opportunities

The GBO would like to make users aware that there are additional proposal opportunities as follows:

High Risk Proposals: As a means of maximizing its scientific impact through cutting-edge observations, the Observatory encourages the submission of high-risk/high-reward proposals.

Filler Programs: Some programs are not time critical or require highly subscribed LST ranges. Such programs may be able to take advantage of “filler” time. There are opportunities for so-called “filler” programs on the GBT.

Further information about each of these programs can be found here.

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