GBT Proposal Guide

Low Frequency Science Opportunities

Low frequency (below 8 GHz) projects, especially those that may require significant amounts of observing time per source or field, are strongly encouraged. Observations up to 200 hours per source or field at low frequencies is not unreasonable for the less subscribed LST ranges. Please see the LST pressure plots in the Proposal Results for previous semesters located here.

Expected GBT available time

The GBT is expected to be shut down from May-September over the next few summers. During these shutdowns repairs to the GBT infrastructure will be performed. This includes azimuth wheel replacement, painting, and track, foundation and grout work.

It is expected that there will be around 2600 hours available for astronomy in the 25B semester with 245 hours available for high frequency observations requiring nighttime conditions (Mustang2, ARGUS and non-VLBI W-band).

We cannot guarantee that monitoring projects can be scheduled due to the planned infrastructure work. The 800 MHz receiver is not expected to be available for monitoring observations in the 26A semester.

Receiver Availability

Ultra-wideband

We will not accept any new proposals requesting the UWBR for the 25B call.

Ku, Q, W-band, and the 342 MHz receivers not available

The Ku, Q, W-band and 342 MHz receivers will not be available in the 25B semester. The Q and W-band receivers are expected to be available for the 26A semester.

Receivers available only during campaigns

The Prime Focus 800 MHz feed will only be available for campaigns during the 25B semester. The 800 MHz feed will be available monthly in the 25B semester. The 800 MHz feed is not expected to be available regularly in the 26A semester.

Receiver available during entire semester

It is expected that the L, S, C, X, KFPA, Ka, Argus and Mustang2 receivers will be available during the entire 25B semester.

GBT Capabilities

The GBO encourages proposals that take advantage of the GBT’s unique capabilities across 0.29 to 116 GHz frequency range. (Coverage is not available for 15.8-18.0 GHz, and 50.5-67.0 GHz).

Key science areas include, but are not limited to:

• low column density HI (NHI ≈10¹⁷ cm^-2 galactic and extragalactic)
• star formation
• fast radio bursts
• galaxy and cluster evolution
• pulsars (searches and timing)
• cosmology
• radio recombination lines
• astrochemistry
• solar system science

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.

Large Proposals

The GBT only accepts large proposals once per year for the B semester proposal deadlines. Large GBT proposals are not accepted at the A semester proposal deadlines. This policy ensures equality for the reviews of all large proposals that can be scheduled across a full year.

Recall that all large proposals are restricted to using no more than 50% of the open skies time available under any weather category (poor, good, excellent) at any LST during any semester.

Regular and Large proposal size definitions for the GBO are as follows:

• 0-8 GHz (Any weather)
  • Regular: < 400 hours and lasting ≤ 1 year
  • Large: ≥ 400 hours or lasting >1 year
• 8-18 and 27.5-50 GHz (Good weather)
  • Regular: < 200 hours and lasting ≤ 1 year
  • Large: ≥ 200 hours or lasting >1 year
• 18-27.5 and > 50 GHz (Excellent weather)
  • Regular: < 100 hours and lasting ≤ 1.5 year
  • Large: ≥ 100 hours or lasting >1.5 year
• Fixed and Monitoring proposals
  • Regular: < 200 hours and lasting ≤ 1 year
  • Large: ≥ 200 hours or lasting >1 year

Proposers submitting Large Proposals should read the Large Proposal Policy to ensure that they address all of the mandatory requirements.

Instrumentation

 The GBT receivers, backends, and observing modes that are available for Semester 2025B proposals are listed in Tables 1 and 2 below.

Receiver	Frequency Range	Expected Availability
Prime Focus 1	290-395 MHz	Not available
Prime Focus 1	680-920 MHz	Monthly 2-week campaigns.
Prime Focus 1	385-520 MHz and 510-690 MHz	Not available
Prime Focus 2	910-1230 MHz	Not available
Ultrawideband Receiver	700-4200 MHz	No new proposals.
L-band	1.15-1.73 GHz	Entire semester
S-band	1.73-2.60 GHz	Entire semester
C-band (linear polarization only – see below)	3.8-7.8 GHz	Entire semester
X-band	7.8-11.6 GHz	Entire semester
Ku-band	12.0-15.4 GHz	Not available.
K-band Focal Plane Array (7 pixels)	18.0-27.5 GHz	Entire semester
Ka-band	26.0-39.5 GHz	Entire semester
Q-band	39.2-50.5 GHz	Not available
W-band	67-93.3 GHz	Not available
ARGUS	75-116 GHz	Entire semester.  See The ARGUS Observer's Web Page for further information
MUSTANG2 (shared-risk – see below)	90 GHz, Shared Risk	Entire semester.  Private instrument – proposals must include instrumentation team (see below).

Table 1

 

Backend	Observing Modes
Versatile Green Bank Astronomical Spectrometer (VEGAS)	Continuum (see below), spectral line, pulsar
Digital Continuum Receiver (DCR)	Continuum
Caltech Continuum Backend (CCB)	Continuum (Ka receiver only).
Mark6 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

Table 2

Permission required for instruments not listed as being available

Anyone requesting a receiver or instrument not listed as being available in the proposal call must have prior permission from the site director, or the GBT schedulers before the proposal is submitted.

C-band Polarization

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

VLBI including the HSA and GMVA

Proposers should clearly justify the need for the GBT 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. 

Proposals requesting the GBT as part of High Sensitivity Array (HSA), and Global 3mm VLBI Array (GMVA) should be submitted through the Very Long Baseline Array's call (available here).

C-band VLBI on the GBT

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

MUSTANG2

The GBO will accept proposals for shared risk observations using the MUSTANG2 instrument at the proposal deadline.  More information on Mustang2 can be found here.  All MUSTANG2 proposals must have permission from the instrument development team – contact Emily Moravec, Simon Dicker or Brian Mason. 

Breakthrough Listen backend

The Breakthrough Listen project is making its backend available for shared-risk observations during the 2025B semester.  The instrument consists of a cluster of 64 Titan X and 1080 GPU-based servers capturing 8-bit baseband voltages over up to 12 GHz of instantaneous bandwidth.  Data rates are typically tens of TB/hr but a pipeline is available to generate spectra with adjustable frequency (> 3 Hz) 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 proposal preparation 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.

Continuum Observations

Proposers wishing to perform continuum observation should consult with a GBO scientist. 

RFI

The most recent RFI monitoring scans for the GBT can be found here.  These scans provide information on the frequencies that may encounter RFI.  Note that a Green Bank computing account is required to be able to view this information.  If you do not have a computing account, please contact the helpdesk to request the desired RFI plots.

Observing and Scheduling Constraints

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.

Mapping

If you are considering mapping with the GBT such that there are major turns or moves (end of rows in raster map, petals in daisy maps, changes 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.

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. 

Scheduling Increments

Please note that the GBT is scheduled in 15 minute (0.25 hour) increments and that all proposals should request time appropriately.   Time requests will be rounded down to the nearest 0.25 hour increment. 

GBT Proposal Preparation

All proposals should state why the GBT is necessary for the requested observations in both the abstract and science justification.

Proposers who need assistance with their proposal should submit a helpdesk ticket via https://help.nrao.edu/.  Proposers needing significant help should submit their requests to the helpdesk well before the deadline.

Proposers are encouraged to look at past proposal call results, especially the LST pressure plots, which can be found in the TAC proposal result reports.  This information can be found here.

 All proposers, including pulsar proposers, should use the GBT Sensitivity Calculator. 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 lessen the chances for error. 

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.

Schools and Workshops

Observer Training Workshops

 

The Green Bank Telescope (GBT) Remote Observer Training Workshop will provide the essential skills and knowledge needed to use the GBT and maximize its scientific output. It is intended for experienced astronomers who need to learn the specifics of observing with the GBT. After completing the workshop, an attendee will be certified to use the GBT as a remote observer. The workshop will focus on hands-on training in the observing techniques most relevant to participants (e.g., high frequency mapping, continuum, pulsar, etc.).

These workshops will be held several times a year and will complement traditional on-site training. 

More information can be found here.

Single Dish Training Workshop

 The Single Dish Training School will provide graduate students, post-docs, and experts in other fields of astronomy with both knowledge and practical experience of the techniques and applications of single-dish radio astronomy using the GBT as the primary example. The school will be based around an intensive series of lectures from experts, as well as hands-on radio-astronomy projects and tutorials. Topics to be covered include radio telescope fundamentals, key single-dish science areas, observing and calibration techniques, the impact of weather, the GBT observing procedures and software, and data reduction.

More information can be found here.