NICER Proposers Guide - Cycle 6

1. Overview

This Announcement of Opportunity (AO), NNH23ZDA001N-NICER, solicits Guest Observer proposals for NICER. Approximately 7.5 Ms of time will be available in the observing period March 1, 2024 to February 28, 2025.

Proposers may request a period of up to 6-months for exclusive use of the NICER 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.

General information about the NICER mission and the X-ray Timing Instrument (XTI) can be found in the NICER Mission Guide document. More detailed information is available on the NICER Documentation page. Tools and files to assist in proposal preparation are available on the NICER Proposal Tools page.

Proposed NICER observations may span both Cycles 6 and 7 (March 1, 2024 - February 28, 2026), but requests for observations extending beyond the end of Cycle 6 in February 2025 must be scientifically justified.

2. Deadline

Proposals are due no later than 4:30 pm ET on September 14, 2023.

3. Proposal Elements and Submission Method

Additional details concerning this observing cycle are given in the NICER AO. There will be a two-phase proposal process. Phase 1 is for observing proposals. Phase 2 is for budget proposals for successful Phase 1 proposers for whom funding is available.

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.
  • Scientific justification in PDF format: The science justification, feasibility, and description of the NICER observing program should not exceed 4 pages. The reference list is not included in that 4-page limit and may be provided on a separate page. In addition, one extra page is allotted to provide a full observing plan for all requested joint observations. These documents should be included in a single PDF totalling no more than 6 pages, which proposers will upload through ARK/RPS.

The following should not be submitted as part of the Phase 1 proposal:

  • The PI's institution's own cover page.
  • Supporting material (e.g., Curriculum Vitae, pending/current support).
  • Formatted electronic copies of the ARK/RPS form.
  • Hard copies of any of the above, including electronically required elements.
IMPORTANT!! For Cycle 4 and thereafter, science justifications should not include information identifying the proposer team. See the Dual-Anonymous Review section for more information.

4. Some Key Details of the Proposal Form

In order to submit a NICER proposal, PIs must first create an ARK account and/or join the NICER RPS group. PIs can then access the NICER Remote Proposal System form via ARK/RPS.

We provide below some key details for this cycle. For further details, consult the ARK/RPS help page for NICER.

Cover Page

  • Provide a title (maximum 120 characters) and abstract (maximum 800 characters) for your NICER 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 NICER RPS form itself.
  • In addition to investigations utilizing NICER observations alone, proposals involving coordinated observations through one of NICER's joint programs may also be proposed during Cycle 6. Proposals for joint program observations should be indicated by checking the appropriate box in the "Joint Proposal?" section of the ARK/RPS form. PIs of joint proposals will also need to input the joint program details for each target in the "Target Form" area below. Descriptions of the nICER joint programs are available here.
  • Institutional endorsement is not required by NASA in NICER phase 1 proposals. If endorsement is required or desired by the PI's institution, contact the NICER help desk for information on how to submit that endorsement.

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.
  • Up to 15 Co-Investigators can be entered into the RPS form. Any additional Co-Investigators can be specified in the team expertise PDF, which should include (again) the complete list of Co-Investigators.
  • In some instances, the PI may wish the first Co-I to serve as a backup for communication regarding the NICER 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.
  • For each target, provide a "Target Category" from the drop-down menu. If no category fits the target type, select the closest, and send email to the NICER help desk with clarification.
  • 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.
    • Background Restricted: Select the maximum background level allowable for the observation, and provide a brief statement justifying that constraint. (See Section 5.)
    • Monitoring Program: For proposals that require two or more observations of the same target (called "visits"), summarize the desired observations, including number, duration, and cadence. Targets can be observed multiple times per day, week, month. etc. Proposed observing programs should use common sense in requesting closely-spaced observations.
    • 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. Phase 0 is defined by the provided Epoch.
    • 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.
    • 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.
    • Minimum Continuous Observation: Provide a justifcation for the desired duration of observation. Note that the maximum continuous observation possible with NICER is time- and location-dependent, and will not exceed 2.4 ks, and is typically much less. (See figure 1 below.)

    See the NICER 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 NICER at the desired observation epoch. Note, however, that Viewing currently evaluates only Sun- and Moon-based constraints, not the full and complex visibility restrictions to which NICER targets are subject. In cases of strict time constraints, proposers may contact the NICER help desk to request a higher-fidelity visibility analysis.
  • If the proposer is requesting NuSTAR time, the minimum NuSTAR exposure time is 20 ks.
  • Estimated Count Rates: Use the WebPIMMS tool to estimate the expected total band (0.2-12 keV) count rate of the source in counts/second for NICER's XTI instrument.
  • Spectral simulation: Users can use WebSpec to simulate XTI spectra with user-selected emission and absorption models.
Distribution of NICER uninterrupted visibility windows
Figure 1: Differential (red) and cumulative (blue) distributions of uninterrupted visible times, effectively averaged over the sky (top) and for a given pointing direction (the Galactic Center; bottom). Because of NICER's location on ISS and the orbital inclination, the inner Galaxy is a somewhat unfavored direction – uninterrupted exposures > 2 ksec are available 30% of the time. For a more typical target, elsewhere on the sky, that fraction rises to > 36% (increasing further for northern declinations). The maximum uninterrupted exposure, given the 93 min orbital period, is ~ 2.7 ksec. However, exposure durations between 800 and 1300 sec are more common.

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.

5. Constraints and Category Designations

NICER observations must take into account a wide variety of complicated observing constraints that can significantly limit visibility to a given source. These constraints include:

  • International Space Station mechanical obstructions, attitude, and operational activities with schedules beyond the control of the NICER mission
  • Sun/Moon/Earth avoidance requirements
  • Increased particle backgrounds from the South Atlantic Anomaly
  • Time-variable particle background at high latitudes associated with disturbances in Earth's magnetosphere due to solar activity.

Observations with additional constraints (time, phase, coordinated, etc.) will need to be designated Category A in order to guarantee inclusion in NICER's schedule during Cycle 6. The effect of time contraints will be evaluated by a member of the NICER technical staff, and their comments provided to the scientific review panel to ensure constraints receive consistent consideration.

Observations of constrained Category B targets will be executed on a best-effort basis. Constrained Category A and B 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.

In summary, the implications for each category designation are:

  • Category A:
    These targets will be observed, even if they require additional scheduling constraints. If these observations cannot be scheduled during Cycle 6, they may be carried over to the next cycle, if appropriate for the scientific investigation.

  • Category B:
    These targets will be guaranteed observing time only if they do not require additional scheduling constraints. If possible, time-constrained Category B observations will be scheduled on a best-effort basis. Category B targets without schedule constraints that do not get observed in this cycle may be carried over to the next cycle, if appropriate for the scientific investigation.

  • Category C:
    These targets will not be guaranteed observing time. Category C targets without schedule constraints will be scheduled on a best-effort basis. Category C targets with schedule constraints are unlikely to be observed.

6. Targets of Opportunity

Observers may propose for identified and anticipated Targets of Opportunity. An identified Target of Opportunity is a target 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). An anticipated Target of Opportunity is an anticipated event which occurs at an unknown time and unknown position (for example, the next Galactic supernova).

To maximize the chance that an identified ToO may be observed during the observing cycle, proposers often propose many targets of a given class, but require only one or some subset of the proposed targets to be observed. For example, a proposal to observe X-ray emission during gamma-ray bright states of blazars may propose 10 blazar targets but require only 1 or two to actually be observed. Therefore target of opportunity proposals of known targets must clearly state, on the ARK target form, the maximum number of ToO triggers required for the proposed science. The ToO proposer must also specify the maximum total observing time for the proposal. For example, a proposal that included 5 ToO triggers, with exposure times of 10, 20, 30, 40, 50 ksec for targets 1-5, but only requires 2 triggers for the proposed science, would have a Maximum Number of Triggers = 2, and a Maximum Total Time Requested = 50 ksec + 40 ksec = 90 ksec.

7. Scientific Justification


  • The scientific justification for a program must not exceed 4 Letter size pages for a non-joint proposal. References are not included in that 4-page limit, and may be provided on a 5th page, if needed. In addition, Joint proposals are allowed one page to discuss the need for joint observations and details of the joint observing program(s). Science justifications may therefore have a length of no more than 6 pages in total. (5 for proposals that do not include joint program observations.)
  • 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.
  • 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 NICER over other existing observatories (preferably linked to some unique characteristic of NICER); 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.
  • PIs are encouraged to review the list of previously-observed targets using the HEASARC Browse interface. Proposals to observe targets already observed by NICER must include a justification for additional observations. Justifications for duplications could include acquiring a much longer exposure, utilizing a different pointing position within an extended object, or sampling a different observing window for a variable object.

8. Dual-Anonymous Review

The overarching objective of dual-anonymous peer review 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. 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 how to write this separate document.

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.

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.
  • NASA understands that dual-anonymous peer review represents a major shift in the evaluation of Guest Observer / Guest 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.

A summary of the key requirements for preparing anonymized Phase-1 proposals is provided in the table below.

AnonymizationPhase-1 proposals are anonymized. Phase-2 (cost) proposals are not anonymized.
SubmissionPhase-1 proposals are submitted through ARK/RPS. Phase-2 (cost) proposals are submitted through NSPIRES.
ReferencesReferences should be in the [1], [2] format.
Proposal length4 pages for NICER science justification. 1 page for references. One additional page for proposals requesting joint observations.
Separate "Expertise and Resources - Not Anonymized" documentThis document provides a list of all team members, their roles, expertise, and contributions to the work. The document should also discuss any specific resources that are key to completing the proposed work.
Additional information may also be found on the web at:

If you have any questions concerning NICER or the NICER GO program, visit the Feedback form.

Last modified: Thursday, 07-Sep-2023 11:14:55 EDT