NRAO Call for Proposals: Semester 2025A

Introduction

The National Radio Astronomy Observatory (NRAO) invites scientists to participate in the Semester 2025A 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 2025A proposals is Wednesday, 31 July 2024, at 17:00 EDT (21:00 UTC).

For the VLA, the D and C-configurations will be available. It is anticipated there will be around 2910 hours on the VLA and 570 hours on the VLBA available for science observing. Opportunities for Joint proposals will be available for ALMA, JWST, 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 D and C configurations.

The NRAO 2025A 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 25A Proposal Call is available here and summarized in the table below:


Date	Action
26 June 2024	NRAO/GBO Call for Proposals
31 July 2024	NRAO/GBO Proposal Deadline @ 17:00 EDT
29 August 2024	Individual Science Reviews Completed
13 September 2024	Science Review Panel (SRP) Meetings Completed
14-15 October 2024	Telescope time allocation committee (TAC) meeting
05 November 2024	Disposition Letters Sent

What's New in 25A?

NRAO and GBO Users' Policies. The policies have been updated ahead of the 25A Call for Proposals.

The NRAO and GBO Users' Policies have undergone several updates:

REMINDER: The Dissertation Plan requirements (Section 7.2) were revised to specify that the plan must be written by the student. The Latex and Word templates are available online.
The text in the Semester Observing Opportunities (Section 3.2.1) to clarify when proposals may be submitted in response to a Call for Proposals, the requirements for proposals are Triggered, and the requirements for those wishing to submit proposals requesting future capabilities.
Clarifications regarding the criteria for Triggered Proposals were made in Sections 3.2.1 and 3.3.2.

See the NRAO and GBO Users' Policies page.

VLBA PST Sessions

Heightened pressure for VLBA time has increased the importance of setting the GST ranges of sessions accurately in the PST and, if possible, avoiding the regions of highest pressure (normally 18:00 – 06:00 GST, around the Galactic center) that can be seen on the pressure plot in the TAC Report.

As detailed in the PST Manual, the sessions defined in the PST are used by the TAC in their assignment of scheduling priorities, thus sessions that pass through high pressure regions are likely to receive a lower scheduling priority than sessions with the same linear-rank science score in regions of lower pressure. In particular, sessions with a 24-hour GST range are guaranteed to pass through high pressure regions and should be avoided if not essential (e.g., for actual 24 hour observations).

The "Guidelines for Creating VLA Sessions" in the PST Manual contain advice that is also useful in creating VLBA sessions; in particular, proposals with a small number of sources should put each target source into a separate session and sources with a large number of sources should be broken into smaller sessions, grouping nearby sources by GST range.

Users are also encouraged to use Sched or Planobs to manually define their GST range as detailed in the Guide to Proposing rather than using the /Calculate Min/Max GST/ button in the PST.

PST Proposal Template

The NRAO now offers an optional Latex template for proposals. Proposers are strongly encouraged to use this template for all proposal types - Regular, Large and DDTs and to follow the appropriate guidelines for font size, page margins and references.

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 25A. 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, the Neutron star Interior Composition ExploreR (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 Configuration Plans and Science Time Available

The July 31, 2024 proposal deadline covers the observing period February 21, 2025 through August 25, 2025 (Semester 2025A), corresponding to the D and C configurations of the VLA. Multi-configuration proposals that include this configuration may also be submitted. Additionally, proposals requesting only configurations that will fall in semester 2025B (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.

Plots of estimated available observing hours as a function of LST for the D and C configurations in semester 2025A are shown below. In these plots, 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 previous configurations and proposals from previous semesters that requested future configurations.

In total, we expect 2910 hours to be available for open skies observing in the 2025A semester; 1461 hours in the D configuration and 1449 hours in the C configuration.

VLA Proposal Types

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 lower frequencies (C-, S-, and L-bands) are particularly encouraged.

Filler proposals can be submitted as Regular proposals or 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 Semester 2025A

For the 2025A 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) has been made 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.

Capability	Description
8-bit samplers	Standard full polarization default setups for: 2 GHz bandwidth continuum observations at S/C/X/Ku/K/Ka/Q bands (16 × 128 MHz subbands) 1 GHz bandwidth continuum observations at L-band (16 × 64 MHz subbands) 256 MHz bandwidth continuum observations at P-band (16 × 16 MHz subbands) 12 MHz bandwidth for Stokes I continuum observations only^* at 4-band (3 × 4 MHz subbands) Dual 4/P-band for Stokes I continuum observations only^* Flexible setups for spectroscopy, using two, independently tunable, 1 GHz baseband pairs, each of which can be split into up to 32 flexibly tunable subbands. Single, dual, and full polarization products for non-default setups. ^*Note: 4-band and dual 4/P-band observations are offered for Stokes I continuum only using standard full polarization default setups. Spectral line and/or polarization science carried out in these bands, or the use of non-standard setups, should be submitted as a RSRO proposal.
3-bit samplers	Standard full polarization default setups for: 8 GHz bandwidth continuum observations at K/Ka/Q-bands 6 GHz bandwidth at Ku-band 4 GHz bandwidth at C/X-bands Flexible setups for spectroscopy, using four, independently tunable, 2 GHz baseband pairs, each of which can be split into up to 16 flexibly tunable subbands. Single, dual, and full polarization products for non-default setups.
Mixed 3-bit and 8-bit samplers	Allows more flexibility for simultaneous continuum and high-resolution spectral line observing.
Subarrays	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).
Y27 or Y1 for VLBI	VLA Phased Array (Y27) or single VLA antenna (Y1) for VLBI. See the VLBA Call for Proposals for more details.
Solar observing	All solar observing except the L-band reverse-coupled system.
On-The-Fly Mosaicing (OTF)	P-, L-, S-, and C-bands only, using linear interpolations in Equatorial Coordinates; no subarrays.
Pulsar	Phase-binned and coherent-dedispersion (YUPPI) pulsar observing, except 4-band YUPPI.

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:

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 semester 2025A, the LWA is expected to be undergoing infrastructure upgrades and availability of the telescopes (LWA1 and LWA-SV) may be limited. Those interested in using this mode should contact Greg Taylor at gbtaylor@unm.edu for more details.

Proposers should be aware that SRO projects will not be carried over to future semesters if they cannot be scheduled for reasons associated with the shared risk component(s) of the observations, even if awarded scheduling 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 and might require lower-level access to the software system (hand-crafted observing scripts, for instance). 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 scheduling priority A, owing to the level of risk associated with these observations. Also, RSRO proposals will not be carried over to future semesters 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 collection of VLITE data during observation can be disabled in the OPT if desired. 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 collection of realfast data can similarly be disabled if desired, by selecting a resource that is not enabled for realfast observing. The third is COSMIC SETI, which enables the search for extraterrestrial intelligence (SETI) using the VLA, and collects data during unconflicted PI science observations. Similar to VLITE, collection of COSMIC SETI data can be disabled in the OPT when setting up 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 Proposal 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 2025A (2025 February 01 – 2025 July 31) or multi-semester proposals.
Global mm VLBI Array (GMVA) proposals for 2025 Session I (2025 April 24 – 29), or later sessions.

VLBA Proposals

It is anticipated that there will be around 570 hours available for new Open Skies proposals on the VLBA in observing semester 2025A. In addition to Regular proposals, Large proposals (those which request 200 hours or more) are welcome on the VLBA. Such proposals should follow the instructions for Large proposals in the NRAO & GBO Users' Policy. It is anticipated that there will be around 150 hours available for new Large proposals on the VLBA in observing semester 2025A. 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.

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.

Science Time Available

The availability of science time varies with GST, with less time available during daytime periods due to maintenance and at other GSTs (in particular in the 18:00 – 06:00 range) due to multi-semester proposals approved at earlier calls that are continuing in 25A. Plots below detail the anticipated time that is available to be allocated for different observing priorities in 25A.

25A VLBA estimated HF availability

The upper plot shows the total estimated availability across all frequencies, while the lower plot shows the estimated availability for high frequency (> 12 GHz) observing. The upper plot also shows the estimated time available by GST hour for large proposals. This is determined by the limitation of time allocated to large proposals to 50% of the open skies time at any given GST and the time already allocated to large proposals from previous calls.

Proposal pressure is a function of both availability and demand. In recent semesters, there has been lower demand in the GST range 06:00 – 18:00 than in the GST range 18:00 – 06:00 (around the Galactic center), leading to lower proposal pressure in the 06:00 – 18:00 range. We expect this trend to continue.

Heightened pressure for VLBA time has increased the importance of setting the GST ranges of sessions accurately in the PST and, if possible, avoiding the regions of highest pressure (normally 18:00 - 06:00 GST, as mentioned above) that can be seen on the pressure plot in the TAC Report.

As detailed in the PST Manual, the sessions defined in the PST are used by the TAC in their assignment of scheduling priorities, thus sessions that include the times of high pressure are likely to receive a lower scheduling priority than sessions with the same linear-rank science score in times of lower pressure. In particular, sessions with a 24-hour GST range (00:00 - 24:00) are guaranteed to pass through high pressure times and should be avoided if not essential (e.g., for actual 24 hour observations).

Users are also encouraged to use Sched or Planobs to manually define their GST range as detailed in the Guide to Proposing rather than using the Calculate Min/Max GST button in the PST.

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.

Observing Capabilities for 2025A

For the 2025A 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 Recently Updated:

The VLBA 3mm sensitivities were updated prior to semester 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:

Capability	Description
Receivers offered	The VLBA has receivers covering the 90cm (P), 50cm (610), 21/18cm (L), 13cm* (S), 6cm (C), 4cm (X), 2cm (Ku), 1cm (K), 7mm (Q) and 3mm (W) VLBI bands * See the Frequency Bands and Performance section of the OSS for details of performance and notes on use
4096 Mbps recording (requires DDC data system)	Available for the 6cm, 4cm, 2cm, 1cm, 7mm, and 3mm receivers^* 1024 MHz polarization-summed bandwidth Available for VLBA, VLBA+Y1, HSA, global VLBI and GMVA We expect to be able to support this recording rate for most of the available open-skies observing time ^*Note: 90cm, 50cm, 21/18cm, and 13cm bands require recording rates of 2048 Mbps or less due to their limited bandwidth
S/X Simultaneous Observations	Up to 4096 Mbps recording rate total across both bands (but with reduced sensitivity). Note that VLA antennas do not have this capability, so S/X cannot be used with VLBA + Y1. See the Frequency Bands and Performance section of the OSS for details of performance and notes on use.
VLBA + Y1	Adds a single VLA antenna (Y1) to the VLBA to provide a short (~50 km) baseline to the VLBA Pt station
Multiple Phase Centers	Up to 300 (or 150) phase centers at 4096 Mbps with a single correlator pass for dual polarization (or full polarization) products
Flexible Frequency Setup with the DDC data system	1, 2, 4, or 8 data channels with bandwidths anywhere from 1 MHz to 128 MHz (all data channels must use the same bandwidth within an observing scan) Data channels may be placed nearly anywhere in the IF
Flexible Spectral Resolution	Up to 4096 spectral channels per data channels for routine DiFX processing Minimum spectral channel spacing of 2 Hz
Spectral Zooming	During correlation, allows the selection of a narrower frequency window to have a large number of spectral channels
Pulsar Modes	Binary gating, matched-filter gating, and pulsar binning correlation modes for pulsar observations

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 capabilities are offered under the SRO program during the 2025A 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.

and 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.

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.

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 2025A in the D (to ~ Feb-May 2025) and C (from ~ May-Aug 2025) configurations, and during reconfigurations. If requesting future semesters, please note that BnA (~ Jan – Feb 2026) 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.

The installed receivers change regularly on the GBT and not all VLBA bands are available every semester. 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 2025A deadline will be considered for scheduling in 2025 Session I (2025 April 24–29), 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 was updated for the 24B semester, so sensitivity calculations from proposals submitted in earlier semesters will need to be re-made.

The GBT is expected to be available for 2025 Session I.

The Apex telescope in Chile is expected to be available at 3mm in 2025 Session I.

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 in a GMVA proposal should be quantitatively justified. Apex, the KVN, or the Greenland Telescope (GLT) must be specified by entering "Apex", "KVN" or "GLT" as "Other" entries in the PST. If the Hancock (HN) or Saint Croix (SC) VLBA antennas (which are not normally included in the GMVA) are requested at 7mm, these should be specified by entering "HN" or "SC" 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.

New GMVA proposals requesting phased ALMA should not be submitted at the semester 2025A deadline. Only proposals which were re-proposed at the Cycle 11 ALMA deadline – those that were approved for GMVA Session 2024/I but failed at ALMA – will be considered.

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 25A.

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 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 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 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 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 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 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

Scientific Justification

The NRAO proposal evaluation and time allocation process is panel based. That is, members of the scientific community are responsible for reviewing proposals based on their scientific merit through the Science Review Panels. As a means of broadening the scientific perspective of its reviewers, and of increasing the participation of the wider astronomy and astrophysics community in the science program of NRAO facilities, SRP membership is deliberately selected to include some colleagues that are not necessarily experts in radio observational techniques. This being the case, we encourage proposers to consider the following when preparing their proposals:

Avoid the use of radio astronomy jargon.
Do not assume the reader is familiar with a particular observing technique - explain it briefly.
Do not assume the reader is familiar with an earlier rationale for a developing line of research - provide adequate historical context and connect the dots as necessary.
Describe previous observations and publications relevant to the proposed observations.
If a particular point source or brightness temperature sensitivity is required, justify it.

Source Lists

The Observatory requires proposers to specify their source lists in full. This enables the Observatory to identify potential conflicts between observing programs and to better understand scheduling pressure on the instruments it operates. It may be the case that the final target list has not been selected at the time a proposal is submitted. In such cases, all potential targets and fields should be listed. The only exceptions to this requirement are for Triggered proposals to observe targets that are unknown a priori. Proposal source lists are not made public by the Observatory.

Dissertation Plans

The Plan of Dissertation is important in the proposal review process and should be well written; it is not a placeholder and should not be a replica of the proposal. The plan must be compliant with specific requirements, which includes following a Plan of Dissertation Research template. See Section 7.2 of the NRAO Users' Policy guide for details.

Useful Resources & Tools

Note: you must be a registered NRAO user to access some of these resources. Please go to NRAO Interactive Services. If you are already a registered user, you are encouraged to update your profile.

Proposal Submission Tool

The Proposal Submission Tool and associated documentation is accessed through NRAO Interactive Services.

Proposal Finder Tool

The Proposal Finder Tool (PFT) may be used to search cover sheets of proposals approved for time on NRAO telescopes. The PFT returns the proposal's authors, title, abstract, and, if available, approved hours.

Very Large Array (VLA)

VLA Observational Status Summary

Very Long Baseline Array (VLBA)

VLBA/HSA Sensitivity (via EVN Sensitivity Calculator)
Observing

NRAO Helpdesk

For help on any aspect of proposing or observing not found in our documentation, please file a ticket with the NRAO helpdesk.