The IXPE (Imagine X-Ray Polarimetry Explorer) GO Program solicits proposals for investigations in any area of astrophysics (not constrained to IXPE’s prime science areas). IXPE Cycle 4 observations will commence on or about February 1, 2027, and continue for a nominal period of 12 months. Individuals may submit proposals for observations that will advance the IXPE mission science return. Observing proposals may be for "standard," "Target-of-Opportunity (ToO)," “Large Program (LP),” or “Multi-cycle” observations. Theory proposals are not solicited. For ToO observations, IXPE anticipates executing approximately 1 high (observations begin within 9 days of trigger) and 7 medium (observations begin between 9 days and 4 weeks of trigger) priority triggers in this GO cycle; hence proposers must strongly justify the response time required to meet the scientific objectives.

The Neutron Star Interior Composition Explorer (NICER) is an X-ray experiment on the International Space Station (ISS) dedicated to high-resolution timing and spectroscopy of rapidly variable X-ray sources in the 0.2–12 keV band. Proposals for NICER data-analysis investigations addressing all areas of astrophysics are solicited, with a limited amount of funding available in GO Cycle 9.

ROSES Amendment 57 announces second opportunities to propose to IXPE and NICER General Observer (GO) programs. The due date for Phase-1 Proposals, submitted via the Astrophysics Research Knowledgebase Remote Proposal System (ARK RPS) for both IXPE and NICER, is 17 September 2026. The text for these two opportunities may be found in Sections 9 and 10 of D.3 Combined General Investigator General Observer Program.

For IXPE, please direct programmatic questions to Hashima Hasan at hhasan@nasa.gov, and technical questions to Kavitha Arur at kavitha.arur@nasa.gov.
For NICER, please direct programmatic questions to Roopesh Ojha at roopesh.ojha@nasa.gov, and technical questions to Keith Gendreau at Keith.C.Gendreau@nasa.gov.