1. Overview

The total amount of time allocated to General Observers during NuSTAR Cycle 12 is expected to be 11.7 Ms (~73% of the total available observing time). This NASA Research Announcement (NRA) solicits General Observer (GO) proposals for NuSTAR, with approximately 8.5 Ms of observing time available during the period from June 1, 2026, to May 31, 2027. Observing time will be made available to scientists at both U.S. and non-U.S. institutions (except the People’s Republic of China). Individuals may submit proposals for three general types of observations: "standard-mode", "Target-of- Opportunity" (ToO), and "Large Programs". An additional 3.2 Ms will be allocated to joint programs through other observatories.

The remaining ~27% of the observing time will be allocated through the NuSTAR Project to the NuSTAR legacy survey observations (2%); NuSTAR PI discretionary time (15%), including unsolicited ToO observations open to the scientific community; and time reserved for calibration observations, engineering tasks, and resolution of operational issues (10%).

NuSTAR data from approved GO program observations (including peer review approved ToO observations) have a nominal six-month exclusive-use period commencing at the time of receipt of the processed data by the observer. Note that Principal Investigators (PIs) may ask for waivers that increase (or decrease) the default exclusive-use period. Waivers should be on a case-by-case basis, infrequent, and always with compelling justification. Data resulting from unsolicited ToO requests will have no exclusive-use period.

Observations of Category C targets will be executed on a best-effort basis. Category C targets not scheduled during a particular observing cycle will not be carried over to the succeeding cycle; such observations may be re-proposed to a future observing cycle.

It is anticipated that no more than $4M in funding will be made available to support the analysis of targets accepted at priority L, A, B or C. Only PIs affiliated with, and located at, a US institution will be eligible for funding for accepted NuSTAR proposals through NASA.

As part of the NuSTAR Cycle 12 program, up to 1.5 Ms of XMM-Newton observing time, up to 150 ks of Swift observing time, and up to 500 ks of XRISM observing time will be made available for coordinated observations with NuSTAR. For more information on joint programs, please see this page.

2. Deadline

Proposals are due no later than January 29 (Thursday), 2026 4:30pm (EST).

Note that the last day to request assistance from the NuSTAR SOC with evaluation of possible stray light contamination, is January 27th, 2026

3. What's New in Cycle 12

New: For Cycle 12, a total of up to 500 ks of XRISM observing time will be made available for joint observations with NuSTAR.

New: For Cycle 12, The minimum response time that may be specified for NuSTAR ToO observations is now < 24 hours, and such a rapid response time must be clearly justified in the proposals. This has been made possible by the development of an automated system that responds to the triggering of these observations, potentially repointing NuSTAR to a ToO target within 6 hours.

New: The scientific justification for all proposals must now include a one-paragraph anonymized work plan.

Reminder: Dual-Anonymous Review Proposals

Reminder: Coordinated Observation Requests

Note that proposers requesting coordinated NuSTAR Cycle 12 observations with any facility have to provide a clear scientific assessment of the need for the NuSTAR exposure, also for the case that coordinated observations turn out not to be possible: Should the NuSTAR observation(s) still be performed? What are the scientific objectives if no coordination is possible?

4. Dual-Anonymous Review and Proposal Evaluation

The overarching objective of dual-anonymous peer review is to reduce bias in the evaluation of a proposal. Under this system, not only are proposers unaware of the identity of the members on the review panel, but the reviewers do not have explicit knowledge of the proposal teams.

Proposers should consult the Guidelines for Proposers to ROSES GO/GI DAPR Programs under "Other documents" on the NSPIRES page for this program element for instructions on writing proposals appropriate for dual-anonymous peer review. The instructions here and in that document supersede the default instructions given in the NASA Grant and Cooperative Agreement Manual (GCAM) and the ROSES Summary of Solicitation. Proposers will also be required to upload a separate "Expertise and Resources Not Anonymized" document, that is not anonymized. The "Guidelines for Proposers to ROSES GO/GI DAPR Programs" contains complete information on how to write this separate document.

To meet the objectives of dual-anonymous peer review, review panels will be instructed to evaluate the anonymized proposals, without initially taking into account the proposing team’s qualifications. As a final check, and only after the evaluation is finalized for all proposals, the panel will be provided with the "Expertise and Resources Not Anonymized" (E&R) document. The panel will review the E&R document to validate that the proposers have the qualifications and capabilities required to successfully execute the proposed science investigation.

• Proposals should eliminate language that identifies the proposers or institution, as discussed in the Guidelines for Anonymous Proposals.
• PIs are required to upload a one-page "Team Expertise" PDF through ARK as a separate upload when submitting the anonymized Scientific/Technical/Management section. (Note that, for NuSTAR proposals, the page limit for the team expertise document is one page, i.e. further constrained compared to "no more than three pages" from the general guidelines document.) This document provides a list of all team members, their institutional affiliations, roles, expertise, and contributions to the work. The document should also discuss any specific resources that are key to completing the proposed work. If a change of the exclusive-use period from the 6-month default is requested (expected to happen infrequently), a compelling justification e.g., protecting the timely completion of a graduate student's thesis, needs to be added in this document.
• NASA understands that dual-anonymous peer review represents a major shift in the evaluation of General Observer / General Investigator proposals, and as such there may be occasional slips in writing anonymized proposals. However, NASA reserves the right to return without review proposals that are particularly egregious in terms of the identification of the proposing team.

Phase-1 proposals will be evaluated by a peer evaluation panel for Merit and Relevance (see Section V(a) of the ROSES Summary of Solicitation), and the evaluation of merit includes:

• The extent to which the proposed investigation complements and enhances the anticipated science return from the NuSTAR mission
• The suitability of using the NuSTAR observatory and associated data products for the proposed investigation, including the degree to which the investigation exploits the unique capabilities of NuSTAR
• The feasibility of accomplishing the objectives of the proposed investigation with the requested observations, including the degree to which the proposal satisfies NuSTAR observational constraints and the feasibility of the proposed analysis techniques
• For joint observing proposals, the relevance and feasibility of the corresponding XMM-Newton, Neil Gehrels Swift or XRISM observations
• The degree to which the proposed observation(s) places demands upon mission resources
• In the case of ToO proposals the justification of the trigger probabilities

5. Large Program Proposals

Data from approved Cycle 12 LPs will have a nominal six-month exclusive-use period after which the data will be placed in the public archive.

An LP may be a ToO but it can only have a single trigger (e.g., where a long observation is needed after an initial trigger).

6. Targets of Opportunity

Proposers interested in submitting ToO requests should note the following:

• Proposals must provide exact, detailed trigger criteria and a credible estimate (including justification) of the probability of triggering the ToO during Cycle 12 (and Cycle 13 for multi-year proposals)
• Proposers must strongly justify the response time required to meet the scientific objectives on the Astrophysics Research Knowledgebase (ARK)/Remote Proposal System (RPS) proposal submission form.

• The minimum response time that may be specified for NuSTAR ToO observations is < 24 hours, and such a rapid response time must be clearly justified in the proposals. This is because an automated system is now in place to respond to the triggering of these observations.

• The standard ToO response time for NuSTAR ToO observations remains 48 hours to 1 week.

• The observations must have an astrophysical trigger and be designated as Category A
• Proposals for ToO observations that can be triggered from a class of objects or set of potential targets are permitted
• Active ToO programs submitted to the Chandra/NuSTAR, XMM-Newton/NuSTAR, Neil Gehrels Swift/NuSTAR, or IXPE/NuSTAR GO Program Calls for Proposals approved prior to the Cycle 12 solicitation will take precedence over NuSTAR Cycle 12 proposals with the same targets and trigger criteria.
• ToO proposals selected as part of the NuSTAR Cycle 12 GO program will take precedence over unsolicited ToO’s and may replace already scheduled observations, even those coordinated with other observatories.
• In the case of Large Program ToOs with multiple observations, only the initial observation is counted against the 1.5 Ms maximum ToO exposure time (since subsequent observations are considered to be monitoring observations).

Multi-year ToO programs may be triggered in Cycle 12 or Cycle 13. Accepted Cycle 12 ToO observations not designated as multi-year can only be triggered until the end of the cycle and observations not triggered during Cycle 12 will not be carried over to Cycle 13. Such observations may be re-proposed to a subsequent cycle. Data from approved Cycle 12 ToO observations will have a nominal six-month exclusive-use period after which the data will be placed in the public archive.

7. Multi-Year Programs

If a multi-year program, in particular one including ToO observations, is not strongly justified in the proposal text it might be evaluated as a Cycle 12-only proposal. No multi-year programs awarded in Cycle 12 will be carried beyond Cycle 13, i.e., all observations must occur in Cycles 12 and 13. Multi-year joint programs with XMM-Newton or Neil Gehrels Swift may also be proposed. However, no XRISM observing time is allowed for multi-cycle proposals. All approved multi-year programs must be category A, B or L. It is anticipated that Cycle 13 will commence on June 1, 2027, and tentatively have a duration of one year.

8. Time-Constrained Observations

• Time-constrained observations designated Category A, B or L will be given highest priority for scheduling during Cycle 12 (or Cycle 12 and 13 for multi-year programs). Time-constrained observations of Category C targets will be executed on a best-effort basis and therefore should be scientifically justified if the time constraint is not satisfied.

• The time constraints for multi-year programs can occur in Cycle 12 and/or Cycle 13.

• Time-constrained Category A, B or L observations that are not part of a multi- year program and are not scheduled during Cycle 12 may be carried over to Cycle 13 where warranted by scientific or operational circumstances (e.g., in the case of coordinated observations with other space- or ground-based observatories). Category C time-constrained observations not scheduled during Cycle 12 will not be carried over to Cycle 13.

• Monitoring programs are defined as investigations requiring two or more observations of the same target, each of which is considered a "visit". For such programs, the time interval between successive visits must be ≥ 14 hours. Note that all monitoring programs are designated as time constrained.

• Proposed Neil Gehrels Swift observing time can include monitoring that precedes, follows, and/or (for ToOs) triggers NuSTAR observing time.

9. Proposal Elements and Submission Method

Additional details concerning Cycle 12 are given in the NuSTAR NRA. There will be a two-phase proposal process. Phase one is for observing proposals. Phase two is for budget proposals for successful phase one proposers who were awarded priority L, A or B targets. Only observing proposals will be accepted at this time.

Proposal submission is done via the HEASARC ARK/RPS on-line system. Hard-copy submission is not required. The following elements are required:

The following should not be submitted:

10. Some Key Details of the Proposal Form

New NuSTAR PIs must first create an ARK account and/or join the NuSTAR RPS group. Having done so, the NuSTAR RPS form can be accessed via ARK/RPS.

We provide below some key details for NuSTAR Cycle 12. For further details, consult the ARK/RPS help file.

Cover Page

• Institutional endorsement is not required by NASA in NuSTAR phase 1 proposals. Use the endorsement-related entries only if they are required or desired by the PI's institution.
• A total of up to 2 Ms of NuSTAR Cycle 12 observing time will be made available for the Large Program (LP) category. The minimum total exposure time for LP proposals is 500 ks.
• In addition to investigations utilizing NuSTAR observations only, proposals involving coordinated observations with the XMM-Newton observatory, XRISM observatory, and/or Swift observatory can also be proposed during Cycle 12. Proposals for joint NuSTAR-XMM-Newton, NuSTAR-XRISM or NuSTAR-Swift observations should be indicated by clicking the Joint proposal section of the ARK/RPS form, and inputting the requested XMM-Newton, XRISM, and/or Swift exposure time in each target form. Proposers may submit the same proposal to XMM-Newton AO-25 and NuSTAR Cycle 12. However, the XMM-Newton AO-25 approved program will be taken into account during the NuSTAR Phase 1 review and duplicate observations of the same targets by NuSTAR will typically not be awarded. Similarly, Proposers may submit the same proposal to Swift AO-22 and NuSTAR Cycle 12 as well as XRISM AO-3 and NuSTAR Cycle 12. However, the Swift AO-22 and XRISM AO-3 approved program will be taken into account during the NuSTAR Phase 1 review and duplicate observations of the same targets by NuSTAR will typically not be awarded. All joint time proposals need to include a NuSTAR component.
For more information on joint programs thourgh NuSTAR, please see the NuSTAR Joint Program Guide page.
• Joint proposals for NuSTAR observations with Chandra or IXPE cannot be submitted in response to this AO. However, NuSTAR does have separate agreements with Chandra and IXPE for coordinated observations. Please see the the joint programs through other observatories section of the Proposals and Tools page for more information.
• Target of Opportunity (ToO) proposals will be accepted in response to this AO.

General Form

• To facilitate checking for conflicts of interest during the peer review process, the co-I's institution must be chosen from the menu (thereby enforcing a uniform set of names). Please check the list of institutions and contact the RPS team as soon as possible if your co-I's institution is not on this list.
• Up to 30 co-investigators can be entered into the RPS form. However, only the first 15 co-investigators will appear on the cover page PDF. The full list will be used by project personnel for conflict checking. Under the Dual Anonymous Proposal Review Procedure reviewers will not see any investigator names provided to ARK/RPS, unless they assess them after ranking the proposals (see the DAPR Guidelines). Please do not enter any investigator names in any ARK/RPS comment fields.
• Proposals involving bilateral work with the People's Republic of China (PRC) and proposals directly from PRC organizations and/or with a PI affiliated with a PRC organization, are not eligible and will be declined without review. For more information see Section III.c of the ROSES Summary of Solicitation.

Target Form

• Time Constrained: A target is considered as "Time Constrained" if any of the following sections of the target form are marked as 'Yes':
  • Position angle dependent
  • Monitoring Program
  • Phase Dependent
  • Date Constrained
  • Multi-year
  See the NuSTAR RPS help page for more information about these fields. In addition, observations coordinated with other ground- or space-based observatories are considered as time constrained.

• Proposers should include a summary of details that are necessary for scheduling and observation planning (constraints, observing mode) in the Remarks box for each target.
• Sources with fluxes > 10^-11 ergs s^-1 cm^-2 within 5° of the target may cause increased non-uniform background gradients due to stray light. Users should check observations for potential stray light contributions using the tool that is available at the NuSTAR SOC web site. If a field is designated as having a "Potential stray light issue", proposers should submit a request for a feasibility analysis to nustar-help@srl.caltech.edu at least 2 business days prior to the proposal submission deadline.
• The minimum exposure for NuSTAR targets is 20 ks. If the proposer is also requesting XMM-Newton, XRISM, and/or Swift time, the minimum exposure times for these telescopes are 5 ks, 10 ks, and 1 ks, respectively.
• Estimated Count Rates: Expected total band (3-79 keV) count rate of the source in counts/second for both modules in a 50% PSF extraction with no deadtime.
• Target of Opportunity (ToOs): A total of up to 1.5 Ms of NuSTAR Cycle 12 observing time will be made available for proposals to observe ToOs. Single-trigger ToOs that are part of a Large Program are not held to a 1.5 Ms exposure time limit. Please note that regular ToOs do not carry over into Cycle 13.

  For ToO observations that are to be triggered from a class of objects: Complete one target form per trigger only, specifying "0.0" for both the R.A. and Dec. fields and providing a generic target name, and, if applicable, enter a list of potential target names in the ToO Remarks field. If the list of targets is too long to fit in the TOO Remarks field, include the list in the anonymized Scientific/Technical/Management section instead and put a note in the ToO Remarks to look there for the list.

  For ToO observations that are to be triggered from a list of specific named objects: Complete one target form per object and trigger criterion even if you ask for time for a subset only. For each ToO proposal the "Maximum Total Time Requested for ToOs" field must be provided. If you ask for time for a subset only, this number will be smaller than the automatically calculated summed exposure time for all target forms.

  Please note that it is the responsibility of the PI of an accepted ToO proposal to alert the NuSTAR SOC when the trigger conditions for their accepted ToO have been satisfied (via http://www.nustar.caltech.edu/page/too_policy).

After completing all fields for a proposal in ARK/RPS, use the Verify button to confirm that all required entries exist and conform to the expected format. Forms that pass verification can then be submitted. ARK/RPS allows PIs to continue to modify submitted proposals until the deadline, so there is no penalty for submitting the proposal form early.

The LaTeX, PostScript, and PDF buttons of ARK/RPS can be used to generate formatted versions of the proposal forms. Although it is often useful for the PIs to keep formatted copies of the forms for the record, it is not a required part of the proposal submission process.

11. Anonymized Scientific/Technical/Management Section

Format

• The anonymized Scientific/Technical/Management section for a standard and ToO Program must not exceed 4 Letter size (8.5" x 11") pages. The anonymized Scientific/Technical/Management section for a Large and/or Joint Program must not exceed 5 pages. Page limits include figures but not references.
• The anonymized Scientific/Technical/Management section can be generated using the software of the PI's choice, as long as it is converted to PDF format before submission. However, the font size and margings should meet the proposal style format requirement described in the ROSES Summary of Solicitation. Specifically, the text body font size should be no smaller than 15 characters per inch. A 12 point font size is recommended. Please note that Phase-1 proposals should have a single-column format. References should be in the [1], [2] format.
• Proposals must not contain hyperlinks to additional material other than references to public information that do not identify the PI, Co-Is or their institutions; web pages with material specific to the proposal such as target lists or stray light assessments are not allowed.
• We suggest that proposers use the LaTeX template or the Word template for the anonymized Scientific/Technical/Management section. When using these templates, the user should double-check that the text area is 6.5" x 9", having at least 1 inch top, botton, right and left margins on US letter size paper (8.5" x 11").

Content

• Proposals should include a description of the scientific objectives; justify the choice of target(s); show that existing data (previous X-ray observations or at other wavelengths) are insufficient to achieve the objectives; justify the choice of NuSTAR over other existing observatories (preferably linked to some unique characteristic of NuSTAR); and demonstrate the feasibility of the proposed observation and analysis.
• Proposals for targets already observed by NuSTAR are allowed, but must include a justification for an additional observation, such as a much longer exposure, different pointing position within an extended object, or different observing window for a variable object. Observed and/or approved NuSTAR targets can be found using the HEASARC/Browse numaster table or by using NuSTAR As-Flown Timeline. A list of approved NuSTAR ToO programs in the NuSTAR, joint NuSTAR/XMM-Newton, joint NuSTAR/Chandra, joint NuSTAR/Swift, and joint NuSTAR/XRISM GO programs can be found on the NuSTAR SOC page.
• Conflicts with Legacy Survey Targets
  Observations of targets accepted through the Cycle 12 Call for Proposals will take precedence over legacy program observations of those targets. The status of legacy survey target observations can be found in HEASARC's numaster table by selecting "EGS", "ELS" or "GLS" for the obs_type keyword.

• The length of the observation should be justified based on the specific scientific objectives, preferably using simulations or scaled from prior NuSTAR observations of a similar source. However, the minimum NuSTAR observing time for a target is set at 20 ksec.
• Proposers should note that NuSTAR's low-inclination (6°), low-Earth orbit allows, on average, a maximum continuous exposure of ~ 3.2 ks per 5.7 ks satellite orbit for targets below a declination |Dec| of ~ 65° for targets at high declination, |Dec| > 65°, the unocculted period may be longer. Unless there is a specific reason why the total elapsed time of an observation is important, proposers should specify only the net exposure time required for achievement of the proposed science goals, excluding observational efficiency factors (Earth occultations and South Atlantic Anomaly passages) in the observing time calculation; specification of the total elapsed time requirement will result in the observation being classified as time-constrained.
• Proposals requesting observations of bright sources (predicted instrument count rate above 100 counts s^-1 for both modules using 50% PSF extraction with no deadtime) with durations > 30 ks are operationally difficult to carry out. Accordingly, such proposals must provide a sufficiently compelling motivation to be considered for acceptance. In addition, proposals requesting observations of bright sources with exposures longer than 75 ks will be considered for implementation only if the total requested time is distributed in multiple observations, each with exposure < 75 ks and separated by more than 1 week.

12. Expertise and Resources - Not Anonymized Document

13. Phase 2 (Budget) Proposals

US PIs whose Phase-1 proposals are assigned a Category A or B rating by the peer review panel or accepted as a Large Program, i.e., Category L, have been invited to submit a Phase-2 (cost) proposal. US PIs of approved proposals with priority C targets only will be eligible for a small flat rate grant, awarded through NASA's Jet Propulsion Laboratory (JPL), if observations are performed. No Phase 2 budget submission is required for these proposals.