IXPE Proposals and Tools: Cycle 1

1. Overview

IXPE solicits General Observer proposals from the general scientific community. Proposals are solicited via NASA's ROSES grant solicitation process. Approximately 11 Ms of time will be available in the observing period February 1, 2024 to January 31, 2025. Approximately 4 Ms of observing time will be allocated for Large Program (LP) proposals. Additionally, Target of Opportunity (ToO) proposals from known targets and theory proposals are also 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. Data from approved LPs will have no exclusive-use period.

As part of IXPE Cycle 1, up to 300 ks of NICER observing time will be made available for joint observations with IXPE.

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. Deadline

For IXPE Cycle 1, proposers are strongly encouraged to submit a Notice of Intent (NOI) through NSPIRES. The deadline for the NOI submissions is September 18th 2023. NOIs are non mandatory, and phase I proposals may be submitted even if an NOI has not been submitted.

Phase I proposals are due no later than 4:30 pm Eastern Daylight Time (EDT) on October 18, 2023.

3. Notice of Intent

The purpose of the IXPE NOI request is to help inform preparations for the peer review. The critical information we seek are the potential number of proposals, the types of proposals, and basic target information. An NOI may be submitted either by the intended PI for the phase 1 proposal or by someone else associated with the proposal. The latter option may be useful for proposals led by individuals not currently registered in NSPIRES. If using this option, please see item #2 below.

One needs first to log into the NSPIRES system. If you don't already have an account, you may create one via the link on the page. Then search for the IXPE announcement using the search box on the page, click on the announcement number, and then click on the Create button. Once a NOI Title has been given on the NSPIRES site, there are 5 Elements to the NOI:

  1. Summary: Please provide a brief description of the target(s) of the intended investigation including, if available, the target name(s), celestial coordinates, and astrophysical object type. For theory proposals, please provide a brief overview of the theoretical investigation. Please note there is a 4000-character limit. Note that the default instructions given on the NSPIRES site are not relevant for IXPE and should be ignored.
  2. Business Data: Please ignore this element unless the person submitting the NOI is not the intended PI for the Phase 1 IXPE proposal. If that is the case, then the intended PI should be entered into the NOI Point of Contact field including that person's name, email address, and phone number.
  3. Budget: This element is Not Requested.
  4. Program Specific Data: Please complete fields 3 and 4 of this element. Fields 1 and 2 may be left blank. If you wish to suggest potential GO review panel members, they may be entered in field 2, however, this is not required.
  5. Proposal Team: Please ignore this element. Specifically, it is not necessary to include any team members on the NOI beyond the intended proposal PI.

4. Proposal Elements and Submission Method

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

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 and Theory proposals and 6 pages (5 pages for text, figures and tables + 1 page for references) for a Large Program and/or Joint NICER 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.

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 1. 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 1 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 coordinated observations with the NICER observatory can also be proposed during Cycle 1. Proposals for joint IXPE-NICER observations should be indicated by clicking the Joint proposal section of the ARK/RPS form, and inputting the requested NICER exposure time in each target form. All joint time proposals need to include an IXPE component.
  • Target of Opportunity (ToO) proposals for known targets will be accepted in this cycle.

General Form

  • Enter the list of Co-Investigators (Co-Is) for your NICER 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.
  • 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. Inclusion of target forms is not permitted for theory proposals.
  • 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.
  • 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.
  • 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

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.

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 1. 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.

8. Targets of Opportunity

Observers may propose for IXPE Targets of Opportunity for targets with known 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). ToO proposals must include a list of pre-defined targets. Such proposals may list a maximum of 6 targets, but require only one or some subset of the proposed targets to be observed. Triggers will only be accepted for targets on the list

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.

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. Scientific Justification - Anonymized


  • The scientific justification for must not exceed 4 Letter size (8.5" x 11") pages for Regular and Theory proposals, or 5 Letter size pages for large program and/or joint IXPE/NICER 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.


  • 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 some unique characteristic 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 justification for additional observations.

10. 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.

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.

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