IXPE Joint Program Guide

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Starting in Cycle 2, IXPE proposers can request joint observations with additional NASA facilities in support of their proposed IXPE observations.The IXPE project has established joint observing programs with NASA's Neutron star Interior Compostion ExploreR (NICER), Nuclear Spectroscopic Telescope Array (NuSTAR) and Neil Gehrels Swift observatory (Swift) to enable IXPE General Observer (GO) proposers to obtain data from any (or a combination) of these facilities together with IXPE for correlated studies. Proposals requesting joint observations must clearly justify the need for the NICER/NuSTAR/Swift observations in order to accomplish the science goals of the proposed IXPE investigation. Details of these joint programs are provided below.

NICER

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 neutron stars and other rapidly variable X-ray sources in the 0.2 - 12 keV band. NICER has made up to 300 ks available to IXPE proposers who wish to take advantage of this opportunity. NICER data acquired through the IXPE GO Program will observe the same exclusive use period as the IXPE data. NICER observations will be scheduled to overlap IXPE observations on a best effort basis. Joint observations with NICER must be receive a Category A to be approved for observations in Cycle 2. No NICER observing time will be awarded without the need for IXPE observing time on the same target. IXPE/NICER Phase-1 proposals selected through this Call for Proposals are eligible for funding solely through the IXPE GO program. The NICER General Observer program will perform feasibility checks on the proposed observations and reserves the right to reject any observation determined for any reason to be technically unfeasible. Such a rejection would likely affect the entire proposed science program and could impact the award of IXPE observing time as well. Selected proposals will be allocated NICER observing time without additional scientific review, if judged technically feasible.

Proposers should carefully review NICER technical documentation available from the NICER proposal webpage.

NuSTAR

The Nuclear Spectroscopic Telescope Array (NuSTAR) Small Explorer mission is the first orbiting telescope to focus light in the high energy X-ray region of the electromagnetic spectrum (E > 10 keV), with an effective bandpass of 3 - 79 keV. The observatory provides a combined improvement in sensitivity and spatial/spectral resolution by factors of 10 to 100 over previous missions that have operated at these energies. NuSTAR has made up to 500 ks available to IXPE proposers who wish to take advantage of this opportunity. Proposals requesting NuSTAR coordinated observations must demonstrate the unique value of adding NuSTAR exposures for the proposed science and present a detailed feasibility case in its support. Joint observations with NuSTAR must be receive a Category A rating to be approved for observations in Cycle 2. No NuSTAR observing time will be awarded without the need for IXPE observing time on the same target.

The requested NuSTAR exposure time per observation (i.e., a single visit to a target) is constrained to a minimum of 20 ks and the time interval between successive visits must be > 14 hours. Sources with fluxes >10^-11 ergs s^-1 cm^-2 within 5 degrees of the target may cause increased non-uniform background gradients due to stray light. Users should check observations for potential stray-light contributions using the tools available at the NuSTAR Target Visbility page. If a field is designated as heavily contaminated, proposers should submit a request for a feasibility analysis to nustar-help@srl.caltech.edu at least two business days prior to the proposal submission deadline.

NuSTAR observations of high count-rate targets (>50 cps/NuSTAR focal-plane module) require special planning and increased downlink capacity. High count-rate observations of duration >30 ks are difficult and can be accepted only if well motivated. High count-rate observations longer than 75 ks will be considered only if the total requested time is distributed in multiple observations, each with exposure time <75 ks and separated by more than 1 week.

Proposers should carefully review NuSTAR technical documentation available from the NuSTAR CalTech website and the NuSTAR proposal webpage.

Swift

The flexibility and multiwavelength capabilities of NASA's Neil Gehrels Swift Observatory can complement and augment some IXPE investigations. The IXPE and Swift teams have established a reciprocal agreement in which Swift observing time up to 200 ks per year is made available for coordinated observations with IXPE. The science investigations supported under this program are restricted to those that are enhanced by the combination of IXPE data and observations using the Swift observatory. Proposals requesting joint Swift observations must demonstrate the unique value of adding Swift exposures for the proposed science and present a full and detailed feasibility case in its support. Joint observations with Swift must be receive a Category A to be approved for observations in Cycle 2. No Swift observing time will be awarded without the need for IXPE observing time on the same target. The award of time shall occur without further scientific review by the Swift mission.

All standard observing restrictions for both observatories will apply to joint proposals under this program. The Swift project will perform feasibility checks on the proposed observations and reserves the right to reject any requests determined to be technically unfeasible for any reason.

Proposers intending to request joint IXPE-Swift observations are strongly encouraged to first review the mission specific information from Swift Technical Handbook or the Swift GI webpage. The Swift Helpdesk and/or the HEASARC Helpdesk can be contacted in case of questions.