Introduction

The National Radio Astronomy Observatory (NRAO) invites scientists to participate in the Semester 2024B Call for Proposals for the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA), High Sensitivity Array (HSA), and Global mm VLBI Array (GMVA).

The submission deadline for Semester 2024B proposals is Wednesday, 31 January 2024, at 17:00 EST (22:00 UTC).

For the VLA, the A-configuration will be available. It is anticipated there will be around 1715 hours on the VLA and 800 hours on the VLBA available for science observing. Opportunities for Joint proposals will be available for ALMA, JWST (see What’s New in 24B?), HST, Swift, Chandra, XMM-Newton, and NICER. Joint Proposals with ALMA or JWST need to be submitted to the facility requesting the larger amount of observing time.

The array configurations available for joint ALMA/VLA will be: ALMA C-1 to C-10 and VLA A, D, and C configurations.

The NRAO 2024B Call for Proposals is for observations with the VLA and VLBA/HSA/GMVA; the corresponding call for the GBT can be found at the GBO Call for Proposals.  

A detailed timeline for the 24B Proposal Call is available here and summarized in the table below:

What's New in 24B?

Joint Programs with JWST.  Starting in 24B, joint proposals may be submitted requesting time on the James Webb Space Telescope (JWST).  A maximum time of 50 hours can be allocated per year on the JWST.

Updated Dissertation Plans.  Students that have dissertation plans as part of their NRAO profile will be REQUIRED to update their plans following a strict thesis template.  The template is available in either Word or LaTex formats (see Section 7.2 of the NRAO and GBO Users' Policies).

As stated in the Users' Policies - While not a guarantee, the Observatory allows reviewers to consider elevating the proposal in the rankings if it is associated with an acceptable Plan of Dissertation. This is given in consideration to the time constraints students typically operate under, as having to resubmit a proposal due to minor criticisms may not be possible within the scope of their studies. Therefore, it is advantageous for students to provide a thoughtful and thorough Plan of Dissertation if their PhD research is reliant on the proposal data.

NRAO and GBO Users' Policies.  The policies have been substantially updated ahead of the 24B Call for Proposals.

   - The requirements and policies concerning Joint Proposals have been significantly revised in Sections 3.2.1 and 3.2.3.
   - The policies for VLA and VLBA Resident Shared Risk Observing (RSRO) and Shared Risk Observing (SRO) have been significantly revised in Section 5.2.
   - The policy for scheduling General Observing (GO) observations has been updated in Section 5.3. 
   - The requirements for student Dissertation Plans have been significantly revised in Section 7.2 (see above).

See the NRAO and GBO Users' Policies page.

VLA Spectral Line.  Starting with the 24B Call for Proposals, the VLA General Observing Setup Tool (GOST) is obsolete. The NRAO requires the use of a proposing specific version of the Resource Catalog Tool (RCT) for proposers requesting spectral-line or non-default VLA WIDAR resources.  See the RCT Proposing page for more details and to access the new proposal specific version of the tool.

Proposal Process and Opportunities

Joint NRAO and GBO Telescope Time Allocation Process

Proposals to the National Radio Astronomy Observatory (NRAO) and the Green Bank Observatory (GBO) for the scientific use of its telescopes are evaluated on the basis of scientific merit and technical feasibility using a panel-based proposal review system.  This joint process is run by the NRAO in accordance with its policy of non-discrimination and inclusion.

Joint Observing Program

Observations that require combinations of the GBT, VLBA, and/or the VLA should submit a proposal for each of the requested telescopes.  The same Scientific Justification should be submitted with each proposal, and it should contain a clear justification for each telescope requested.  VLBI proposals which request the GBT or VLA as elements of the VLBI array do not need separate proposals.  For more details see the Joint Proposal page.

Access to joint observations with external facilities will continue for the VLA, VLBA and GBT for semester 24B. This includes joint observations with ALMA, the James Webb Space Telescope (JWST), the Hubble Space Telescope (HST), the Swift Gamma-Ray Burst MIssion, the Chandra X-ray Observatory, the XMM-Newton Project, NICER, and the Fermi Gamma-ray Space Telescope. For more details see the Joint Proposal page.

Director's Discretionary Time Including Education and Public Outreach

Proposals for Director's Discretionary Time (DDT) may be submitted at any time. They must be submitted through the PST. DDT proposals are intended to address targets of opportunity, high-risk/high-return exploratory time, or other science opportunities deemed sufficiently urgent to justify prompt action. 

DDT proposals may also be submitted for the purpose of education and public outreach---for example, to image an iconic source or to support an educational opportunity for students. Such proposals should clearly justify the requirements for the requested time allocation and observing mode on any given instrument, and should describe the anticipated impact of the observation.  

While there is not an a priori limit to time that can be requested via DDT, it is expected that no more than 5% of the available science time on each telescope will be allocated for this purpose.

Other Proposal Opportunities

The NRAO 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.
• Commensal Observing: Commensal observations can be an effective way to maximize observing hours on NRAO telescopes, by allowing multiple experiments or systems to run simultaneously, when resources allow.  The Observatory may support two kinds of commensal observing:  commensal observing projects, and commensal systems.  For more information see the Commensal Observing with NRAO Telescopes page.
• Filler Programs: Some programs are not time critical, not strongly dependent on array configuration, or do not require highly subscribed LST ranges. Such programs may be able to take advantage of "filler" time.   The proposal should make clear in the abstract and early in the science justification that "filler" time is being requested.  If “filler” time is requested, the proposal will be ineligible for scheduling priority A or B.
  

Further information about each of these programs can be found on the Proposal Opportunities page.

VLA Proposal Guide

VLA Proposal Types 

It is anticipated there will be around 1715 hours available on the VLA in observing semester 2024B. In addition to Regular Proposals, Large proposals (those which request 200 hours or more) are particularly encouraged and welcome on the VLA. Such proposals should follow the instructions for Large proposals in the NRAO & GBO Users' Policy. Large proposals which require multi-semester observations are often supported. Filler proposals are also encouraged – these are scientifically useful programs, preferably utilizing the lower frequency bands of the VLA, that can be scheduled over a large range of LST using short (2 hours or less) scheduling blocks. Such projects can help to fill gaps in the dynamic observing schedule. Programs requesting time at L-band (specifically HI 21 cm programs) are strongly encouraged.

Filler proposals can be submitted as Regular proposals or even Large proposals (the Users' Policy instructions for Large proposals still apply); either Large or Regular filler proposals can be multi-semester proposals if scientifically justified. Filler proposals should be explicitly identified as such and will normally only be considered for filler time (i.e., priority C) regardless of their ranking. See the instructions for Filler Programs in the NRAO & GBO Users' Policy for further information.

VLA Configuration Plans and Science Time Available

The January 31, 2024 deadline nominally covers the observing period October 18, 2024 through February 3, 2025 (Semester 2024B), encompassing the A configuration of the VLA. Multi-configuration proposals that include this configuration may also be submitted. Additionally, proposals requesting only configurations that will fall in semester 2025A (or later) may be submitted if the Principal Investigator is a graduate student. NRAO offers this service to provide scientific and technical feedback for students, and to provide them with an opportunity to re-submit their proposals for their principal semester with this information in hand. Students should ensure that their status is up to date and correct in the NRAO User Database. Please refer to the VLA Configuration Plans for details and availability of upcoming configurations.

The plot of estimated available observing hours as a function of LST for the A configuration in semester 2024B is shown below. In this plot, engineering, maintenance, and testing cause the solid (upper) line to be less than the total number of LST days in this configuration; such activities occur predominantly during daytime.  

Estimated science time available per LST hour is shown by the solid (upper) black line for all frequencies, the dashed (middle) line for K-band conditions, and dotted (lower) line for Q-band conditions. The colored bars show pre-committed time where green represents priority A, yellow priority B, and red priority C. The lighter green, yellow, and red represent high frequency (HF; K through Q bands) priority A, B, and C, respectively. For the net available time in this configuration per LST hour subtract the bars of the pre-committed time from the black curve. The pre-committed time in this plot consists of A-priority not completed in the previous A configuration and proposals from previous semesters that requested future configurations.

Observing Capabilities for Semester 2024B

For the 2024B semester the General Observing (GO) capabilities are given in the Offered VLA Capabilities during the Next Semester section of the Observational Status Summary (OSS) and are summarized in the following table. Several additional capabilities are available to proposers through the Shared Risk Observing (SRO) and Resident Shared Risk Observing (RSRO) programs, as described below.

Important Update: Starting with the 24B Call for Proposals, the VLA General Observing Setup Tool (GOST) is obsolete. The NRAO requires the use of a proposing specific version of the Resource Catalog Tool (RCT) for proposers requesting spectral-line or non-default VLA WIDAR resources. For more details and to access the new proposal specific version of the tool, please visit https://go.nrao.edu/pst-rct.

Both single pointing and mosaics with discrete, multiple field centers are supported. Data rates up to 60 MB/s (216 GB/hour) are considered GO. Correlator integration time limits per band and per array configuration also apply as described in the OSS. The data rate and total data volume required by a proposal will be a consideration in its technical evaluation.

There are some limitations on frequency settings and tuning ranges, especially at Ka-band; please consult the OSS for further details. Additionally, the Exposure Calculator is available to estimate sensitivities, while other special tools are available to assist users with the development of correlator setups for the proposal deadline (see VLA Proposal Submission Guidelines). All antennas employ electronics and receiver systems that provide continuous frequency coverage from 1–50 GHz in the following observing bands: 1–2 GHz (L-band); 2–4 GHz (S-band); 4–8 GHz (C-band); 8–12 GHz (X-band); 12–18 GHz (Ku-band); 18–26.5 GHz (K-band); 26.5–40 GHz (Ka-band); and 40–50 GHz (Q-band). In addition to these, all VLA antennas are equipped with 200-500 MHz (P-band) and 54-84 MHz (4-band) receivers near the prime focus.

We continue to offer shared risk programs to our user community for those who would like to push the capabilities of the VLA beyond those offered for general use.

VLA Shared Risk Observing

The VLA Shared Risk Observing (SRO) program allows users access to capabilities that can be set up via the Observation Preparation Tool (OPT) and run through the dynamic scheduler without intervention, but are not as well tested as GO capabilities. Data rates higher than 60 MB/s (216 GB/hour) and up to 100 MB/s (360 GB/hour) are considered SRO. In addition, the following capabilities are offered under the SRO program during this semester:

• Up to 3 independent subbarrays using standard 3-bit continuum setups, or a mix of standard 3-bit and standard 8-bit continuum setups, and up to 3 independent subarrays with changing standard continuum setups in a given subarray (e.g., to perform reference pointing at X-band for high frequency observations).
• On-the-Fly (OTF) mosaicing for X-, Ku-, K-, Ka-, and Q-bands (used when each pointing on the sky is no more than a few seconds), but not using subarrays.
• Wideband VLA for VLBI: Enables recording of VLA WIDAR continuum-mode correlations during VLA phased array (Y27) VLBI observations. Currently, this only supports standard VLA 8-bit continuum modes with a 2-GHz bandwidth. See the VLBA Call for Proposals for more details.
• eLWA: Joint LWA and VLA 4-band observations using a single 8 MHz subband centered at 76 MHz, and 4-bit VDIF output.
  Note: During semesters 2024A and 2024B, LWA1 is undergoing infrastructure upgrades and will likely not be available for this observing mode, which will leave only LWA-SV to join VLA observations. For 2025 and after, three LWA stations in New Mexico are expected to be available in this observing mode.

Proposers should be aware that SRO projects will not be carried over if they cannot be scheduled for reasons associated with the shared risk component(s) of the observations, even if awarded priority A.

See the VLA Proposal Submission Guidelines for information about tools and other advice on proposing for Shared Risk observing capabilities.

VLA Resident Shared Risk Observing

The VLA Resident Shared Risk Observing (RSRO) program provides access to extended capabilities of the VLA that require additional testing. This access is provided in exchange for a period of residence to help commission those capabilities. Users are encouraged to conceive and propose innovative ideas for new VLA capabilities. Some staff suggestions can be found at the VLA RSRO program section of the VLA OSS.

Proposers should be aware that RSRO projects are generally not approved at priority A, owing to the level of risk associated with these observations. Also, RSRO proposals will not be carried over if they cannot be scheduled, similar to SRO proposals.

A detailed description of the VLA RSRO program is available at the VLA Proposal Submission Guidelines web page.

Commensal Observing Systems at the VLA

There are currently three commensal systems in operation on the VLA that may take data at the same time as your proposed observation. The first is the VLITE system, which will take data at P-band during regular observations that use bands other than P-band. Hence, VLITE is turned off by default during P-band or dual 4/P-band observations. The VLITE system is deployed on up to eighteen VLA antennas. Observers wishing to gain access to the commensal VLITE data taken during their VLA observations should follow the instructions on the VLITE web page for doing so. The second is the realfast system, which takes data at very fast dump rates in an effort to detect Fast Radio Bursts (FRBs). This system is fully commissioned for observing at L- through X-bands, in parallel with standard continuum correlator configurations. The third is COSMIC SETI, which enables the search for extraterrestrial intelligence (SETI) using the VLA, and collects data during unconflicted PI science observations. For information about commensal observing see the Commensal Observing with NRAO Telescopes page.

Proposal and Observation Preparation

Proposal preparation and submission are via the Proposal Submission Tool (PST) at NRAO Interactive Services. Use of the PST requires registration in the NRAO User Database. There are various tools and documentation to help users in this process. Descriptions of all updated documentation and tools, along with an outline of the steps required to write a proposal, are available at the Guide to Proposing for the VLA web page.

When constructing sessions in the PST, proposers should be cognizant of their use by the Telescope Time Allocation Committee (TAC). Specifically taking into account the time available as a function of LST, software will assign an initial scheduling priority to each session in each proposal, which can be modified by the TAC if they desire. The assigned scheduling priority will depend on the linear-rank score of the proposal from its scientific review, the LSTs involved in the session (daytime is harder to accommodate than nighttime, for instance), the predicted atmospheric conditions for observing over that LST range at the time of year of the configuration, the total time requested in the session, and the competition from other proposals requesting time at similar LSTs. Please see this description for guidance on how to set up sessions in the PST, and this document for a complete description of the VLA Prioritizer (the software that generates the initial scheduling priorities for all sessions that are subsequently used by the TAC to derive the final priorities).

All approved VLA observations are set up using the Observation Preparation Tool (OPT). Most projects will be observed dynamically; users granted dynamic, non-triggered time, must either submit their scheduling blocks before the start of the configuration or contact the VLA Scheduler (schedsoc@nrao.edu) before that date to avoid a reduction in scheduling priority. Early submission maximizes the opportunity of them being observed and helps us to schedule the VLA most efficiently. Advice on the optimal length of scheduling blocks and other useful information may be found at the Observing FAQ web page.

Information about VLA capabilities, proposal preparation and submission, observing strategies, and calibration overhead can be found in the VLA Observational Status Summary, at the Guide to Proposing for the VLA, and at the Guide to Observing with the VLA. Answers to Frequently Asked Questions are contained in these proposing and observing guides. Questions may also be directed to the NRAO Helpdesk.

VLBA, HSA and GMVA Guide

Proposal submission information for the following three combinations of telescopes are detailed in individual sections below:

• Very Long Baseline Array (VLBA) and High Sensitivity Array (HSA) proposals requesting time in Semester 2024B (2024 August 01 – 2025 January 31) or multi-semester proposals.
• Global mm VLBI Array (GMVA) proposals for 2024 Session II (October 10 – 15), or later sessions, including proposals requesting the GMVA with ALMA for 2025 Session I (spring; date T.B.D.).

VLBA Proposals

The VLBA is a truly unique facility that provides unprecedented, ultra-high angular resolution for studying a wide range of astrophysical phenomenon. Sources that may be studied by the VLBA include, but are not limited to:

• Non-thermal continuum emission, including polarimetry, from active galactic nuclei (AGN), Galactic micro-quasars, pulsars, and other sources.
• Maser emission lines of OH (1.7 and 6.0 GHz), CH₃OH (6.7 and 12.2 GHz), H₂O (22 GHz), SiO (43 and 86 GHz) and other molecules, and numerous thermal absorption lines, in a variety of Galactic and extragalactic circumstances.
• Multiple-phase-center surveys across the primary beam.
• Parallax and proper motion via differential astrometry of a variety of stars, star-forming regions, and nearby extragalactic objects, at accuracies as good as 10 microarcsec.
• Absolute astrometry at accuracies of ~200 microarcsec to expand the International Celestial Reference Frame.

Overall information about the VLBA is available in the VLBA Observational Status Summary (OSS); specific sections relevant to various proposal types are linked below.

VLBA proposals must be prepared and submitted using the NRAO Proposal Submission Tool (PST), accessible via NRAO Interactive Services. Use of the PST requires registration by all proposers, including co-investigators, in the NRAO User Database.

Approximately 800 hours of VLBA observing time are expected to be available for new Open Skies proposals in observing semester 2024B. In recent semesters, there has been less proposal pressure in the GST range 06:00 – 18:00 than in the GST range 18:00 – 06:00, and we expect this trend to continue.

Most approved VLBA observations are performed dynamically; for those dynamic observations, users must either submit their observing (.key) files (to vlbiobs@nrao.edu) before the beginning of the semester (February 01 or August 01 for A and B semesters, respectively), or contact the VLBA Scheduler (schedsoc@nrao.edu) before those dates to avoid a reduction in scheduling priority. Early submission of schedules maximizes the opportunity of dynamic observing and assists in the efficient scheduling of the VLBA.

VLBA Large and Filler Proposals

Large proposals (those which request 200 hours or more) are particularly encouraged and welcome on the VLBA.  Such proposals should follow the instructions for Large proposals in the NRAO & GBO Users' Policy.  Large proposals which require multi-semester observations are often supported.

Filler proposals are also encouraged – these are scientifically useful programs, preferably utilizing the lower frequency bands of the VLBA, that can be scheduled over a large range of GST, require fewer than eight VLBA stations, and use short (2 – 6 hours) scheduling blocks.  Such projects can help to fill gaps in the dynamic observing schedule.  Filler proposals can be submitted as Regular proposals or even Large proposals (the Users' Policy instructions for Large proposals still apply); either Large or Regular filler proposals can be multi-semester proposals if scientifically justified. Filler proposals should be explicitly identified as such and will normally only be considered for filler time (i.e., priority C) regardless of their ranking. See the instructions for Filler Programs in the NRAO & GBO Users' Policy for further information.

Observing Capabilities for 2024B

For the 2024B semester the General Observing (GO) capabilities are given in the Offered VLBA Capabilities during the Next Semester section of the Observational Status Summary (OSS) and are summarized in the following table. Several additional capabilities are available to proposers through the Shared Risk Observing (SRO) and Resident Shared Risk Observing (RSRO) programs, as described below.

New and Updated:

• The VLBA 3mm sensitivities have been updated for 24B. The new values have been included in the EVN calculators and can be found at Frequency Bands and Performance in the OSS. 

The GO capabilities being offered are:

The VLBA operates two data systems, a Polyphase Filterbank (PFB), and a Digital Downconverter (DDC). These are described in detail in the Roach Digital Backend (RDBE) section of the VLBA OSS, which also includes suggestions for selecting the optimal observing system for various scientific goals. For the best continuum sensitivity (i.e. 4096 Mbps) at most receiver bands, or for the most flexible observing setups, the DDC is the better choice. For continuum observations using the 20cm or 13cm receiver bands, the PFB provides a setup using 2048 Mbps that can reduce the impact of prevalent radio-frequency interference (RFI). It is worth noting that while the DDC mode provides wider bandwidth (4096 Mbps recording) and tuning flexibility, the PFB mode (2048 Mbps recording) provides more accurate amplitude calibration and should be used if <10% flux density accuracy is required.

Proposals requiring significant additional correlator resources, such as multiple phase centers per field or multiple pulsar phase bins, should consider mechanisms to support the correlation without adversely affecting the throughput of other projects. These should be entered in the technical justification section of the proposal.

VLBA Shared Risk Observing

The VLBA Shared Risk Observing (SRO) program allows observers access to capabilities that are essentially commissioned, but are not well tested. The following capability is offered under the SRO program during the 2024B semester:

• Baseband Data Copy: Limited amounts of raw data recorded at each station can be copied to user-supplied media for correlation at a different location. See the VLBA OSS SRO section for more details.

For HSA observations only: 

• Wideband VLA for VLBI: Enables recording of VLA WIDAR continuum-mode correlations at full 2-GHz BW during VLA phased array (Y27) VLBI observations. See the HSA Station Notes for more details.

Proposers should be aware that SRO projects will not be carried over if they cannot be scheduled for reasons associated with the shared risk component(s) of the observations, even if awarded priority A.

VLBA Resident Shared Risk Observing

The VLBA Resident Shared Risk Observing (RSRO) program provides users with early access to new capabilities in exchange for a period of residency in Socorro to help commission those capabilities. For example, the phased-VLA system was developed through RSRO programs. Users are encouraged to conceive and propose innovative ideas for new VLBA capabilities. Some staff suggestions, such as VLBA real time correlation, can be found at the VLBA RSRO program section of the VLBA OSS. For details about participating in the RSRO program, see the RSRO Considerations section of the Submission Guidelines page in the Guide to Proposing for the VLBA.

Users wishing to propose a RSRO program should select the VLBA RSRO observing mode in the resources section of the PST in order to submit their proposal as a RSRO program. 

Proposers should be aware that RSRO projects are generally not approved at priority A, owing to the level of risk associated with these observations. Also, RSRO proposals will not be carried over if they cannot be scheduled, similar to SRO proposals.

High Sensitivity Array (HSA) Proposals

The HSA comprises the VLBA, phased VLA, GBT, and Effelsberg telescopes. Similar to the VLBA, all of the HSA stations can observe at 4096 Mbps (General Observing). The EVN Observation Planner or old EVN Calculator can select 4096 Mbps for HSA sensitivity estimates. Details on the HSA telescopes are documented in the HSA section of the VLBA OSS, and special considerations on proposing and observing are listed in the HSA page of the Guide to Proposing for the VLBA.

VLBI observations combining the VLBA with any one or more of the other three HSA stations can be requested in a single HSA proposal. HSA proposals requesting only VLBI use of HSA telescopes should not be identified as Joint proposals. However, separate proposals must be submitted for any non-VLBI use of any requested telescopes.

HSA proposals must be prepared and submitted using the NRAO Proposal Submission Tool (PST), accessible via NRAO Interactive Services. Use of the PST requires registration by all proposers, including co-investigators, in the NRAO User Database. The inclusion of HSA stations should be quantitatively justified in the proposal. 

HSA Station Notes

• The phased Very Large Array (Y27) will be available for HSA observing in Semester 2024B in the B (to ~ Sep 2024) and A (from ~ Oct 2024) configurations, and during reconfigurations. Note that BnA (~ Sep – Oct 2024) configuration is reserved for VLASS therefore scheduling HSA observations during BnA may be difficult. Please note that high frequencies (at receiver bands 22 GHz and above) have better phasing in the more compact configurations (C and D). High frequency phasing in the extended configurations in the summer can be quite difficult. For more details, see VLBI at the VLA.

Wide-band correlation of VLA-only data in parallel with the VLBI recording is offered as Shared Risk Observing (SRO). This supports standard VLA 8-bit continuum modes with a 2-GHz bandwidth. If your science requires these wide-band correlations, you should explain this and justify your need for wide-band correlations in the top box of the Technical Justification of your proposal in the PST. Proposals for recording wide-band correlation of VLA-only data using modes other than standard VLA 8-bit continuum with 2-GHz bandwidth can be submitted as Resident Shared Risk Observing (RSRO) proposals; see the VLBA RSRO section of the OSS for details of the RSRO program.

• The Green Bank Telescope (Gb): Proposers should clearly justify the need for the GBT in the text of the proposal. All proposers requesting the GBT should include any needed setup and overhead time in the total time request for their proposals.

Observations using the GBT 6-cm (C band) receiver as part of the HSA must be taken, correlated, and calibrated in full Stokes mode. Due to the large cross-talk between polarizations, only total intensity (Stokes I) data will be usable. 

Please see the GBT proposal call for receiver availability, time availability, and other relevant factors regarding the GBT's participation in HSA observations.

• The Effelsberg (Eb) 100-m telescope supports both the PFB and DDC observing systems available on the VLBA. Consult this web page for more detailed information about the Eb HSA station.

Global mm VLBI Array (GMVA) Proposals

GMVA proposals submitted for the semester 2024B deadline will be considered for scheduling in 2024 Session II (October 10–15), or later sessions.

Complete information on the GMVA is available at the GMVA website. Ongoing special considerations are documented in the GMVA section of the VLBA OSS; new features and/or special cases are cited here.

As noted in the VLBA section above, the VLBA sensitivity at 3mm has been updated so sensitivity calculations from proposals submitted in previous semesters will need to be re-made.

NOTE: The GBT will not be available for observations with the GMVA for 2024 Session II but is expected to be available for 2025 Session I (e.g., for observations proposed at this deadline including ALMA with the GMVA).

GMVA proposals must be prepared and submitted using the NRAO Proposal Submission Tool (PST), accessible via NRAO Interactive Services. Use of the PST requires registration by all proposers, including co-investigators, in the NRAO User Database. The inclusion of the GBT and/or ALMA in a GMVA proposal should be quantitatively justified. ALMA, the KVN, or the Greenland Telescope (GLT) must be specified by entering "ALMA", "KVN" or "GLT" as "Other" entries in the PST. Proposers should use the EVN Observation Planner tool to determine their sensitivities and upload the PDF summary or summaries on the Technical Justification page of the PST. 

NOTE: The 3mm noise estimates provided by the Observation Planner (and the old EVN Sensitivity Calculator) use SEFD values determined during reasonably good weather and while the antennas were performing well. Because real-world conditions are often less than ideal, the actual noise levels obtained during observations may be significantly worse.  This is especially true for GMVA observations, which are observed on fixed dates and cannot be rescheduled due to poor weather.  When planning for GMVA observations, users are encouraged to assume the actual noise will be roughly 3 times higher than the tool’s estimate.

Observations at 7mm with the VLBA antennas can be scheduled as part of a GMVA program during what would otherwise be gaps in observing while other antennas are making pointing or calibration observations. Such observations can be included in GMVA proposals.

The GMVA will record at the highest bit rate which instrumentation and resources permit. Currently all telescopes will record at 4096 Mbps.

An opportunity to propose VLBI observations using the phased ALMA telescope in conjunction with the GMVA is available at this Call for Proposals:

It is expected that phased ALMA will participate in some GMVA observations during ALMA Cycle 11 (~Oct 2024 - Sept 2025; it is anticipated that the ALMA Cycle 11 Call for Proposals will be open in April 2024). GMVA session I in 2025 (tentatively scheduled for April 24–29) should provide an opportunity for GMVA + ALMA observing. In ALMA Cycle 11, ALMA expects to support 3mm and 7mm VLBI observations. Spectral line VLBI is supported at both wavelengths, so GMVA + ALMA spectral line observations can be proposed.

Proposers should:

• specify "ALMA" in the Other Stations text field in the PST
• select the default GMVA 3mm or 7mm observing mode of 4096 Mbps, dual polarization
• specify the amount of time and GST range(s) needed for ALMA separately, either in Session Constraints or Comments, or in the Technical Justification.

A separate proposal to ALMA must also be submitted at the deadline for ALMA Cycle 11 proposals. For this, all proposers (PI and Co-Is) must be registered ALMA users (see the ALMA science website).

Restrictions on GMVA+ALMA proposals in Cycle 11:

• GMVA observations with ALMA will be limited to a fixed recording mode, which currently provides 4096 Mbps on all baselines.
• Direct phasing of the ALMA array is limited to targets with a correlated flux density > 0.5 Jy at 3mm or > 0.35 Jy at 7mm, contained within an unresolved core on ALMA baselines up to 1 km. Direct phasing on the science target ("active" phasing) thus puts a lower limit on the brightness of the science target.
• For weaker sources, ALMA offers the option of "passive" phasing. In this mode, the ALMA is phased on a bright phasing calibrator close in angular distance to the science target. (This mode has been in use for VLBI at the VLA for many years). The phasing calibrator has to be brighter than 0.5 Jy at 3mm (>0.35 Jy at 7mm) and be located within 6 degrees from the science target (<10 deg at 7mm). Proposers must specify the phasing calibrator in their proposal; consult the ALMA calibrator catalog.
• In order to make a clean linear-to-circular polarization transformation of ALMA recordings, any target source must be observed at each frequency for a duration of at least 3 hours (breaks for calibrators permitted) to sample a range of parallactic angles.
• Large ALMA Programs (>50 hours of observing time) are not permitted because phased ALMA is a non-standard mode.
• No long-term programs may be proposed, and no proposals will be carried over into the next cycle.
• As time for ALMA observations with the GMVA will be scarce, proposals should include a quantitative justification as to why ALMA is essential for the goals of the project.

Documentation and Assistance

Detailed information about the VLBA instrument, its capabilities, observing strategies, proposal preparation and submission, and observation preparation, can be found in the VLBA Observational Status Summary, at the Guide to Proposing for the VLBA, and at the Observing with the VLBA web pages. Questions should be directed to the NRAO Helpdesk.

Joint Proposals

Joint Proposals Between the VLA, GBT, and VLBA

Observing programs that require combinations of the GBT, VLBA, and/or the VLA should submit a proposal for each of the requested telescopes. The same Scientific Justification should be submitted with each proposal, and it should contain a clear justification for each telescope requested.  The proposals will be reviewed and considered jointly by the Telescope Time Allocation Committee. VLBI proposals which request the GBT or VLA (or any other HSA telescope) 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.

Joint Proposals with External Facilities

Here we list opportunities for joint proposals with several external (non-AUI) facilities.  Agreements for Joint Observations with external facilities were made at different times across the boundaries when the NRAO was split into multiple observatories (NRAO, GBO, and LBO) in 2017, and when the LBO was reintegrated back into the NRAO in 2019.  Therefore, the agreements below will sometimes mention various combinations of the NRAO, GBO, and LBO.  Regardless, access to the Joint Observing program will continue for the VLA, VLBA, and GBT for semester 24B.

Joint Observations with JWST

By agreement between the NRAO and the Space Telescope Science Institute (STScl), detailed in a Memorandum of Understanding, the NRAO can award up to 50 hours of JWST observing time per year.  In return, STScI can award up to 5% of the NRAO scientific observing time on the VLA, VLBA, and GBT. Proposals for joint NRAO and JWST observations must be submitted to the observatory where more observing time is being requested.  N.B., specific technical information must be supplied for the Partner Observatory.   See the Joint Observations with JWST page for details.

Joint Observations with NICER

By agreement between the NRAO and NASA, detailed in a Memorandum of Understanding, the NRAO can award up to 250 ksec of NICER observing time per year.  In return, NICER can award up to 5% of the NRAO scientific observing time on the VLA, VLBA, and GBT or up to 200-300 hours per year on each telescope.  See the Joint Observations with NICER page for details.

Joint Observations with ALMA

By agreement between the NRAO and the Joint ALMA Observatory (JAO), detailed in a Memorandum of Understanding, the NRAO can award up to 50 hours on the ALMA 12-m array, 50 hours on the 7-m array, and 50 hours on the Total Power array per cycle.  In return, the JAO can award up to 5% of the available time on the VLA per year. Proposals for joint NRAO and ALMA observations must be submitted to the observatory where more observing time is being requested.  N.B., specific technical information must be supplied for the Partner Observatory.  See the Joint Observations with ALMA page for details, including the available array configurations.

Joint Observations with XMM-Newton Project

By agreement with the NRAO and GBO Observatories, detailed in a Memorandum of Understanding, the XMM-Newton Project may award up to 3% of NRAO/GBO open skies observing time.  Similarly the NRAO/GBO Time Allocation Committee may award up to 150 ks of XMM-Newton time per year.  See the Joint Observations with XMM-Newton page for details.

Joint Observations with Chandra X-ray Observatory

The community has the opportunity to propose for observing time on NRAO facilities through a joint program with the Chandra X-ray Observatory.  Proposers to the NRAO have the opportunity to request time on Chandra, to be awarded on the recommendation of the NRAO Telescope Time Allocation Committee (TAC) and approved by the NRAO Director. Up to 120 ksec will be made available to NRAO proposers annually.  The NRAO has allocated up to 3% of the open skies observing time on the VLA, the VLBA, and the GBT for Chandra joint proposals.

Due to Chandra's increasingly challenging thermal constraints, the amount of Chandra exposure time available for High Ecliptic Latitude (HEL) targets with |bGal| > 55deg is extremely limited.  If you request joint time on Chandra, please avoid long exposures on such targets if at all possible.  You must note explicitly the requested amount of Chandra HEL time in the body of your science justification.  N.B., Chandra ToO proposals are not supported under the Chandra-NRAO joint program.  See the Joint Observations with Chandra page for details.

Joint Observations with the Hubble Space Telescope (HST)

By agreement between the NRAO and the Space Telescope Science Institute, STScI can award up to 3% of the available time on NRAO's North American facilities to highly ranked proposals that request time on both HST and NRAO telescopes.  In return, STScI has offered 30 orbits of HST time for allocation by the NRAO TAC per year.   N.B.,  HST "Snapshot" observations are not supported under the HST-NRAO Joint program since there is no guarantee that Snapshot targets will be completed.  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 has been established, detailed in a Memorandum of Understanding. By this agreement, the Swift Program permits NRAO to award up to 300 kiloseconds of Swift observing time per year.   Similarly, NRAO permits the Swift Guest Investigator (GI) Program to award no more than 5% of the NRAO scientific observing time on the VLA, GBT and VLBA, or up to 200-300 hours per year on each telescope.  See the Joint Observations with Swift page for details.

Joint Observations with Fermi Gamma-ray Space Telescope

It is possible to propose for observing time on NRAO facilities through the Fermi Gamma-ray Space Telescope Joint Proposal Opportunity or the Cooperative Proposal Opportunity.  A maximum of 5% of the NRAO open skies observing time is made available on the VLA, the VLBA and the GBT, or up to 200-325 hours per year on each telescope.  See the Joint Observations with Fermi page for details.

Tips for Proposers

Useful Resources & Tools