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IXPE Cycle 3 Guide for Proposals

1. Overview

IXPE solicits General Observer proposals from the general scientific community. Proposals are solicited via NASA's ROSES grant solicitation process. It is anticipated that Cycle 3 will commence on February 1, 2026, and have a duration of one year. Cycle 3 and subsequent GO cycles are subject to the result of the Senior Review to be conducted in 2025. Approximately 11 Ms of time will be available in the observing period February 1, 2026 to January 31, 2027. Approximately 4 Ms of observing time will be allocated for Large Program (LP) proposals. Target of Opportunity (ToO) proposals are solicited in this call.

Proposers may request a period of up to 6-months for exclusive-use of the IXPE data associated with their proposal. The exclusive-use period will commence upon delivery of the data to the HEASARC, typically within two weeks of the observation. If an exclusive-use period is not requested, the validated data will be made public via the HEASARC archive within two weeks of acquisition.

As part of IXPE Cycle 3, up to 300 ks of NICER observing time, 500 ks of NuSTAR observing time, 200 ks of Swift observing time and 200 ks of XRISM observing time will be made available for joint observations with IXPE. Additionally, up to 5% of 'open skies' time on the Karl G. Jansky Very Large Array (VLA), Very Long Baseline Array (VLBA), and Robert C. Byrd Green Bank Telescope (GBT) facilities (or up to 200-300 hours per year on each telescope) will be made available through a joint program with NRAO. For more information on joint programs, please see this page.

General information about the IXPE mission can be found on the IXPE Mission page. More detailed information is available on the IXPE Support Documentation page. Tools and files to assist in proposal preparation are available on the IXPE Proposal page.

2. What's New in Cycle 3

  • Legacy Projects are added to IXPE's mission goals.
  • For Cycle 3, up to 200 ks of XRISM observing time will be made available for joint observations with IXPE.
    • In Cycle 3, proposals requesting joint XRISM time should justify their request under the assumption that the gate valve is closed.
  • For Cycle 3, Up to 5% of 'open skies' time on the Karl G. Jansky Very Large Array (VLA), Very Long Baseline Array (VLBA), and Robert C. Byrd Green Bank Telescope (GBT) facilities (or up to 200-300 hours per year on each telescope) will be made available for joint observations with IXPE.
  • Joint Proposals with NICER are not solicited this cycle.
  • For more information on joint programs, please see this page.
  • In this cycle, ToO proposals involving both known and unknown targets (e.g., 'the next millisecond accreting X-ray pulsar') continue to be solicited.
  • Proposals for theoretical investigations are not solicited this cycle. Theoretical investigations that propose to aid in the interpretation of IXPE results are encouraged to propose to Science Mission Directorate's Astrophysics Theory Program and/or other appropriate funding sources.
  • Beginning in Cycle 3, multi-cycle proposals with IXPE are solicited. Proposals may request that observations be scheduled over a three-cycle period. A total of up to 1 Ms of GO time may be awarded to multi-cycle proposals over the three-cycle period, with no more than 400ks of time individually in Cycles 4 and 5. Multi-cycle proposals cannot request ToO observations. Multi-cycle joint programs with NICER, NuSTAR, Swift, XRISM or NRAO may not be proposed.
  • Updates to ToO response times:
    • High: IXPE observations to begin within 9 days of the receipt of the ToO trigger request
    • Medium: IXPE observations to begin between 9 days to 4 weeks from the trigger request
    • Low: IXPE observations to begin after 4 weeks from the trigger
  • The scientific justification for all proposals must now include a one paragraph anonymized work plan.

3. Deadline

Phase I proposals are due no later than 4:30 pm Eastern Daylight Time (EDT) on September 11, 2025.

4. Proposal Elements and Submission Method

Additional details concerning Cycle 3 are given in the IXPE call for proposals. There will be a two-phase proposal process. Phase-1 is for observing proposals. Phase-2 is for budget proposals for successful and elgible phase one proposers who were awarded priority A or C targets.

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

  • Proposal form (cover page & general form, and one or more pages of the Target form) generated by, and submitted through, ARK/RPS.
  • The page limit for the anonymized Scientific/Technical/Management section in PDF format, not exceeding 5 pages (4 pages for text, figures and tables + 1 page for references) for Regular proposals and 6 pages (5 pages for text, figures and tables + 1 page for references) for a Large Program, Multi-cycle and/or Joint Program proposal, to be uploaded through ARK/RPS.
  • One-page "Expertise and Resources - Not Anonymized" PDF is requried through ARK as a separate upload when submitting the anonymized Scientific/Technical/Management section.

The following should not be submitted:

  • The PI's institution's own cover page.
  • Supporting material (e.g., pending/current support).
  • Formatted electronic copies of the ARK/RPS form.
  • Hard copies of any of the above, including electronically required elements.

Phase-2 (cost) proposals must be submitted through the NASA NSPIRES electronic proposal website by an Authorized Organizational Representative of the proposing organization according to the instructions in the ROSES Summary of Solicitation. The cost proposal will consist of a Budget Details (maximum of two pages) section and a Narrative section (maximum of two pages) with a detailed justification of all proposed items for funding. Proposal content, including the list of investigators, must remain consistent between Phase-1 and Phase-2 proposals.

5. Key details of the proposal form

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

We provide below some key details for IXPE Cycle 3. For further details, consult the ARK/RPS help file.

Cover Page

  • Provide a title (maximum 120 characters) and abstract (maximum 800 characters) for your IXPE proposal. The Principal Investigator's name, institution, address, telephone and email address should be already populated. Incorrect information should be corrected within the PI's user profile, not in the RPS form itself.
  • Institutional endorsement is not required by NASA in IXPE phase 1 proposals.
  • IXPE Cycle 3 observing time will be made available for proposals in the Large Program (LP) category. The minimum total exposure time for LP proposals is 1.5 Ms. Proposals requesting a total exposure time larger than 1.5 Ms will be classified as Large Programs
  • In addition to investigations utilizing IXPE observations only, proposals involving joint observations with the NICER,NuSTAR, Swift, XRISM and/or NRAO observatories can also be proposed during Cycle 3. Proposals for joint observations should be indicated by clicking the Joint proposal section of the ARK/RPS form, and inputting the requested exposure time (as well as other information for the observations) in each target form. All joint time proposals need to include an IXPE component. For more information on joint programs, please see this page.
  • Target of Opportunity (ToO) proposals for known and unknown targets will be accepted in this cycle.

General Form

  • Enter the list of Co-Investigators (Co-Is) for your proposal. 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 Help Desk as soon as possible if your Co-I's institution is not on this list.
  • In some instances, the PI may wish the first Co-I to serve as a backup for communication regarding the IXPE proposal. In this case, the "Contact First Co-Investigator" box must be checked, and a telephone number provided. If the box has not been checked, communications regarding the proposal will be routed ONLY through the PI.
  • Proposers may request, and must justify, an exclusive-use period of up to 6 months; by default, validated data are made available in the public HEASARC archive within two weeks of acquisition with no exclusive-use period. Proposal merit is evaluated without regard to whether or not exclusive use is requested. Requests for an exclusive-use period MUST be noted on the proposal cover sheet and justified in the "Expertise and Resources Not Anonymized" document. See Section 12 for more details.
  • Please note that bilateral collaborations between scientists affiliated with institutions from the USA and the People's Republic of China (PRC) are not allowed by United States Federal law. Multilateral collaborations that involve scientists from institutions in the USA, the PRC, and other countries are allowed, however. Please refer to the PRC FAQ for ROSES for details.

Target Form

  • To begin adding targets to the Target Form, select the green "Add" button. Multiple blank targets may be added by selecting the number of desired targets from the drop-down. Once a target has been added, it may be cloned.
  • For each target, provide a "Target Category" from the drop-down menu. If no category fits the target type, select "Other".
  • Estimated Count Rates: Use the WebPIMMS tool to estimate the expected count rate of the source in counts/second in both the total band (0.5-10 keV) and the 2.0-8keV band for the polarization for IXPE.
  • The requested time per observation (i.e., a single "visit" to a target) is constrained to a minimum of 10ks.
  • WebPIMMS can also be used to calculate the Minimum Detectable Polarization. Proposers are strongly encouraged to read the instructions for using WebPIMMS to estimate MDP99 before performing their calculations.
  • For each target, select the checkbox next to "Yes" for the following conditions if they are applicable:
    • Extended Source: Provide the extent of the source in arcminutes.
    • Coordinated Observation: Use drop-down to indicate if the coordination is required, or simply a preference. Provide the observatory/observatories that will need to be involved in scheduling. Desribe the nature of the coordination and a summary of the constraints that coordination adds to the observation.
    • Phase Dependent: For objects with periodicities where the timing of the observation depends on the orbital phase, provide parameters needed to calculate the desired phase interval.
    • Time Constrained: For observations tied to specific events or that have other specific requirements for the duration and/or observing cadence, summarize the timing constraints with sufficient detail to facilitate scheduling of the observation.
    • Target of Opportunity: If the target will be observed based on a triggered condition, provide the expected trigger probability for the period covered by this cycle (1 year), and a brief summary of the requested requested follow-up observations. Note that the maximum exposure time that can be requested for a single ToO trigger is 1.5 Ms. If a proposal requires multiple triggers of the same or different targets, the total observation time requested may be higher.
  • See the IXPE RPS help page for more information about these fields. In addition, observations coordinated with other ground- or space-based observatories add complexity to the observation scheduling, and will thus require higher priority in order to be scheduled. See Section 7 for more details.
  • Time-constrained sources should be evaluated with the Viewing tool to determine if the source is visible by IXPE at the desired observation epoch.

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.

6. Dual-Anonymous Review and Proposal Evaluation

The phase-1 proposal review will be done in a dual-anonymous fashion. The overarching objective of Dual-Anonymous Peer Review (DAPR) is to reduce unconscious bias in the evaluation of the merit 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. In order to meet the objectives of dual-anonymous peer review, review panels will be instructed to evaluate the anonymized proposals based on their scientific merit, without initially taking into account the proposing team's qualifications. As a final check, and only after the scientific evaluation is finalized for all proposals, the panel will be provided with the "Expertise and Resources - Not Anonymized" documents. The panel will validate the qualifications of the team in order to allow the reviewers to assess the team capabilities required to execute a given proposed science investigation.

Proposers should consult the "Guidelines for Anonymous Proposals" document in the "Other Documents" section on the NSPIRES page of 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 Guidebook for Proposers and the ROSES Summary of Solicitation. Proposers will also be required to upload a separate "Expertise and Resources - Not Anonymized" document, which is not anonymized. The "Guidelines for Anonymous Proposals" document contains complete information on writing proposals appropriate for a dual-anonymous reviews.

Key factors for PIs to keep in mind are:
  • Proposals should eliminate language that identifies the proposers or institutions, as discussed in the Guidelines for Anonymous Proposals.
  • PIs are required to upload a one-page "Expertise and Resources - Not Anonymized" PDF through ARK as a separate upload when submitting the science justification. This document must not be anonymized. 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.
  • NASA understands that dual-anonymous peer review represents a major shift in the evaluation of General Observer 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.

Additional information may also be found on the web at: https://science.nasa.gov/researchers/dual-anonymous-peer-review.

Phase-1 Proposals will be evaluated by a peer evaluation panel with respect to Relevance and Merit, as defined in Section 12 of the NASA Grant and Cooperative Agreement Manual (GCAM). In addition, the evaluation of a proposal shall include:

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

7. Constraints and Category Designations

Accepted IXPE observation proposals will recieve either a Category A or Category C designation.

Observations with additional constraints (time, phase, coordinated, etc.) will need to be designated Category A in order to guarantee inclusion in IXPE's schedule during Cycle 3. The effect of time contraints will be evaluated by a member of the IXPE technical staff, and their comments provided to the scientific review panel to ensure constraints receive consistent consideration.

Constrained Category A observations not scheduled during the cycle may be carried over to the following cycle where warranted by scientific or operational circumstances (e.g., in the case of coordinated observations with other space- or ground-based observatories). Category C observations not scheduled during the cycle will not be carried over to the following cycle.

Note that accepted ToOs that are not executed will not be carried over to the following GO cycle. Untriggered ToO observations may be re-proposed to a future observing cycle. Such resubmitted proposals should ensure no language that identifies the proposers or institutions is included

8. Targets of Opportunity

Observers may propose for IXPE Targets of Opportunity for targets with either known or unknown right ascension and declination, to be observed during an anticipated event which occurs at an unknown time or duration (for example, a radio outburst from Cyg X-3, or the next millisecond accreting X-ray pulsar).

Proposers interested in submitting ToO requests should note the following:
  • Proposals must provide exact and detailed trigger criteria and a credible estimate (including justification) of the probability of triggering the ToO during Cycle 3. For ToO proposals of known targets, the celestial coordinates must be provided.
  • The observations must have an astrophysical trigger and receive a Category A rating.
  • A maximum of 6 targets may be listed.
  • Proposals must assign a priority to each ToO target based on the requested response time from the time of the trigger. These priorities are defined as
    • High: IXPE observations to begin within 9 days of the receipt of the ToO trigger request
    • Medium: IXPE observations to begin between 9 days to 4 weeks from the trigger request
    • Low: IXPE observations to begin after 4 weeks from the trigger
  • Each ToO trigger is limited to a maximum exposure of 1.5 Ms.
  • Proposers may request a maximum of 3 ToO triggers per proposal.
  • IXPE anticipates executing approximately 1 high and 7 medium triggers in this GO cycle, hence proposers must strongly justify the response time required to meet the scientific objectives. There are no limits on the number of low priority ToO observations.
  • Accepted ToOs that are not executed will not be carried over to the following GO cycle. Untriggered observations may be re-proposed to a future observing cycle. Such resubmitted proposals should ensure no language that identifies the proposers or institutions is included.

It is the responsibility of the Principal Investigator (PI) of an accepted ToO proposal to alert the IXPE Science Operations Center when trigger conditions for their accepted ToO have been met. Such ToO observations are triggered by the PI via the IXPE ToO web site. Prior to submission of this form, the PI should verify the visibility of the target using the viewing tool.

The IXPE mission is designed to execute only one ToO observation per month, except in very unusual circumstances. ToO observations will be executed on a best effort basis. IXPE's response to a ToO depends on visibility constraints and when the ToO trigger is received with respect to the weekly planning cycle. Note that the highest priority ToOs triggers are particularly difficult to handle at night and on weekends when the Mission Operations Center is not staffed. These should be avoided in all but the most urgent cases.

9. Large Program Proposals

The IXPE GO program also solicits proposals for the Large Program (LP) category in Cycle 3. Approximately 4 Ms of observing time is allotted for LPs. The minimum total exposure time for LP proposals is 1.5 Ms. Proposals requesting a total exposure time larger than 1.5 Ms will be classified as Large Programs. LPs are NOT eligible to make requests for an exclusive-use period. A LP may include multiple targets, up to a maximum of 6 targets. Approved LP’s are ranked as Category A programs.

Proposers are encouraged to submit large program proposals covering the following topics as part of legacy projects:

  • Deep observation of a rapidly rotating stellar-mass black hole in the soft state to search for EVPA rotation versus energy as predicted in General Relativity
  • Deep observation of the Crab pulsar to constrain the emission zone geometry thereby advancing our understanding of the pulse emission mechanism
  • Observation of a high accretion rate AGN to determine the Comptonizing medium geometry
  • Additional studies of stellar-mass BH X-ray transients through all outburst phases to measure the evolution of the accretion geometry
  • Observation of a bright outburst of an accreting millisecond X-ray pulsar suitable for constraining the magnetic field geometry and improving constraints on the NS equation of state
  • Observation of a magnetar in outburst to search for definitive signatures of vacuum birefringence
  • Extended campaign on Her X-1 to measure the coupling between the crust superfluid and the crust itself

10. Multi-cycle Proposals

In Cycle 3, proposals may request that observations be scheduled over a three-cycle period. A total of up to 1 Ms of GO time may be awarded to multi-cycle proposals over the three-cycle period, with no more than 400ks of time individually in Cycles 4 and 5. The Cycle 3 review may award up to 1 Ms of GO time in each of Cycles 4 and 5. In addition, proposers may wish to note that their observation(s) could be carried out over multiple Cycles if required for mission planning purposes. Please note that this is allowed only for non-ToO proposals and those do not include joint observations. If this is the case, the Science justification should include text similar to the following: “The proposed observations may be performed over multiple cycles."

Proposers interested in submitting multi-cycle proposals should note the following:
  • Multi-cycle programs must be strongly justified in the proposal text. If a multi-cycle program is not strongly justified in the proposal text it might be evaluated as a Cycle 3-only proposal.
  • No multi-cycle programs awarded in Cycle 3 can request time also in Cycles 4 and/or 5.
  • Multi-cycle proposals cannot request ToO observations.
  • Multi-cycle proposals cannot request Joint observations.
  • All approved multi-year programs must recieve a category A rating.
  • A separate Target forms be should be created for each Cycle for which observing time is requested. In each Target Form, the cycle during which the observation is to occur must be indicated in the Other Remarks field. Please refer to the RPS help page.

11. Scientific Justification - Anonymized

Format

  • The scientific justification for must not exceed 4 Letter size (8.5" x 11") pages for Regular proposals, or 5 Letter size pages for large program, multi-cycle and/or joint proposals. One additional page may be used for references.
  • Proposals must use a font having no more than 15 characters per inch (horizontally), typical of 12-pt Times New Roman font. The scientific justification can be generated using the software of the PI's choice, as long as it is converted to PDF format before submission.
  • 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 are not allowed.
  • We suggest that proposers use the LaTeX template or the Word template for the scientific justification. When using these templates, the user should double-check that the top, bottom, right and left margins are at least 1 inch.

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 IXPE over other existing observatories (preferably linked to the unique polarimetric capabilities of IXPE); and demonstrate the feasibility of the proposed observation and analysis.
  • The length of the requested observation should be justified based on the specific scientific objectives, preferably using simulations or scaled from prior observations of a similar source. Use the WebPIMMS tool to estimate the expected total count rates and minimum detectable polarization.
  • PIs are encouraged to review the list of previously-observed targets using the HEASARC Browse interface. Proposals to observe targets already observed by IXPE must include a strong justification for additional observations.
  • The scientific justification for all proposals must include a one paragraph anonymized work plan.

12. Expertise and Resources - Not Anonymized

PIs are required to upload a one-page "Expertise and Resources - Not Anonymized" document PDF through ARK as a separate upload when submitting the anonymized Scientific/Technical/Management section. (Note that, for IXPE 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 an exclusive use period is requested, this must be strongly justified in the "Expertise and Resources Not Anonymized" document. Criteria for an exclusive-use period include, but are not limited to, the following:

  • Data are needed for a soon to be completed graduate student thesis: request justification needs to include the names of the student and advisor, how close the student is to graduating, and the importance of the IXPE data to the thesis research.
  • Personal reasons (e.g., parental leave, health-related, etc.).
  • Particularly complex data reduction challenges.

This document will be distributed to the review panel after all proposals have been reviewed and rated, only for programs which are in the selectable range. This is to allow the reviewers to assess the team capabilities required to execute a given proposed science investigation. If there are clear, compelling deficiencies in the expertise required to see through the goals of the proposal, the panel may decide to flag the submission accordingly, and provide a detailed justification in its comments to NASA. This review may not be used to flag "up" proposals for having strong team qualifications, nor may it be used to re-evaluate or upgrade proposals.

IXPE Helpdesk

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