Chandra Announcement: Chandra Cycle 25 Call for Proposals Released

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Tara Gokas

Dec 15, 2022, 11:37:10 AM12/15/22
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Chandra Cycle 25 Call for Proposals Released 15 December 2022

The CXC is pleased to announce the release of the Chandra Cycle 25 Call for Proposals (CfP). The Call for Proposals, Proposers' Observatory Guide (POG), proposal planning software, and general information are posted on the "Proposer" web page at the CXC website:

Proposals are due: Wednesday 15 March 2022 at 6PM (US Eastern Daylight Time)

What's New in Cycle 25

Statement concerning HRC operation: Proposers should be aware that the HRC instrument (both HRC-I and HRC-S) has had limited use since Feb 2022 due to anomalies in its electronics that began in Nov 2020. A backlog of previous Cycle HRC observations remain in the Long Term Schedule. Only two short science observations have been executed on each instrument since Feb 2022 (all performance was nominal) and operations henceforth are restricted to only one of two redundant electronics circuits. As of the time of this CfP, a return to science plan has been approved with implementation to begin no earlier than 13 Feb 2023. While all hopes and expectations are that an HRC return to science operations will be fully successful, proposers may wish to consider other possible observing strategies in their plans.

Observing proposals utilizing HRC in any capacity will continue to be peer reviewed based on scientific merit and the suitability of using the Chandra X-ray Observatory without considering possible contingencies.

TOO Proposals will now be reviewed in TOO Topical Panels: Starting in Cycle 25, TOO proposals will be reviewed by TOO Topical Panels. In previous cycles, TOO proposals were reviewed by subject-specific Topical Panels along with non-TOO proposals. Starting in Cycle 25 TOOs will be reviewed in panels considering only TOO proposals and including panelists with diverse scientific backgrounds. TOO proposers are advised to bear in mind that some panelists from outside the area of expertise will be reviewing proposals.  

Changes for Multicycle Proposals: 

  • Multicycle proposals are no longer limited to time-constrained programs. 

  • Any multicycle proposal requesting at least 400 ks in any cycle or a total exposure of 1 Ms or more must be submitted as a Large or Very Large Proposal.

  • All multicycle proposals will require either a Monitor Constraint that spans the multi-cycle duration or a Window Constraint for each cycle with assigned exposure times. The Window Constraints of a multicycle proposal in the Chandra Proposal Software (CPS) tool default to the nominal calendar year for each cycle (Jan-Dec). The proposer can adjust those Window Constraints to restrict or expand the scheduling flexibility. If the multi-cycle observing strategy requires additional Window Constraints, the proposer should consider using a Monitor Constraint or indicating the additional Window Constraint(s) in the Target Remarks and selecting "Yes, required" for "Are there additional constraints in the remarks?" in the CPS

Changes to the Joint Program: A new joint program opportunity is now available with the James Webb Space Telescope (JWST). 150 hours of JWST observing time are available for this opportunity. A total of 300 ksec of Chandra observing time is available for award as part of the annual JWST Call for Proposals. 

There are reductions to the joint program with the Hubble Space Telescope (HST). 150 orbits of HST observing will be available for this opportunity. A total of 600 ksec of Chandra observing time is available as part of the annual HST Call for Proposals.

As in previous cycles, proposers wishing to take advantage of the JWST and HST joint programs with Chandra are encouraged to submit their proposal only to the observatory announcement that represents the primary science. Please refer to Chapter 5 of the CfP for further details. 


Maximum number of counts for all non-grating ACIS observations: all non-grating ACIS observations are now required to provide an estimate of the maximum expected number of counts for any individual spectrum that will be scientifically analyzed from this observation. If the spectral analysis will be segmented in any form (e.g., by time or spatial region), a proposer should indicate the segment with the most counts, not the aggregate total. Proposers will indicate this information in the Chandra Proposal Software tool. 

Reference list will no longer count against the total page limit: references should now appear on a separate page at the end of the scientific justification and technical feasibility. The single reference page does not count against the page limits and must only contain references (no figures, no tables, no charts, and no narrative text of any kind).

Web-based Star Checker: The increased operating temperature of the Aspect Camera Assembly (ACA) has affected its ability to acquire faint guide stars. A new web-based tool is available to help proposers determine roll angles and dates that have suitable fields for guide star acquisition given a target and offset configuration. Proposers are strongly advised to use the tool to determine the feasibility of their targets:

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