XRISM Joint Programs Guide

---

XRISM proposers can request joint observations with other missions in support of their scientific goals. Such proposals must cleary justify the neccessity of joint observations to accomplish scientific objectives. Joint proposals are not necessarily simultaneous or coordinated between facilities; any such constraints must be separately specified and justified in the observing proposal. Currently, joint programs are available with NuSTAR and XMM-Newton.

XMM-Newton

ESA's XMM-Newton mission provides simultaneous soft X-ray high resolution spectroscopy in the 0.4-2 keV band with the Reflection Grating Spectrometers (RGS) that match XRISM Resolve's capabilities in the hard band for point sources, high throughput low resolution imaging spectroscopy in the 0.3-12 keV band with European Photon Imaging Camera (EPIC) CCDs cameras with 15arcsec PSF (HEW), and optical/UV observations with the Optical Monitor (OM).

Up to 200 ks of XMM-Newton time will be available to XRISM observers in Cycle 3. Proposals for joint TOO observations are allowed within this allocation. However, no XMM-Newton observations with a reaction time of less than five working days from the trigger date can be considered. It is the responsibility of the PI to inform both observatories immediately if the trigger criterion is fulfilled.

Proposers must provide the following additional XMM-Newton-related information as part of their XRISM proposal:

• choice of prime instrument
• the requested exposure time, justification for the exposure time, target count rates, and assumptions made in their determination
• information on whether the observations are time-critical.

Establishing technical feasibility is the responsibility of the observer, who should review the XMM-Newton documentation. All standard observing restrictions apply to joint proposals. For proposals that are approved, the XMM-Newton project will perform detailed feasibility checks; they reserve the right to reject any approved observation that is in conflict with safety or schedule constraints, or is otherwise deemed to be non-feasible. ESA's XMM-Newton SOC will contact successful PIs after the XRISM peer review results have been announced to specify observational details.

NuSTAR

NASA's NuSTAR mission provides low resolution imaging spectroscopy in the 3-79 keV band with 58 arcsec PSF (HPD).

Up to 500 ks of NuSTAR time will be available to XRISM observers in Cycle 3. The response time for NuSTAR TOO observations can be less than 24 hours with automated rapid response, while XRISM's is 48 hours. Thus, if scientifically justified, NuSTAR can start observing a TOO or a time-constrained source before XRISM does. The minimum exposure that can be requested for any NuSTAR observation is 20 ks. A technical description of NuSTAR, and considerations important for proposers can be found at NuSTAR proposal page.

Proposers must provide the following additional NuSTAR-related information as part of their XRISM proposal:

• the total requested NuSTAR observing time
• the expected NuSTAR count rates based on simulations
• an evaluation of possible stray light contamination obtained by using the NuSTAR target constraint check available on the NuSTAR SOC website.

If the target stray light evaluation indicates "Potential Issues" then proposers may submit a request for a feasibility analysis to the NuSTAR SOC at nustar-help@srl.caltech.edu. The request should include the target name and/or J2000 RA Dec coordinates for the observation. If the NuSTAR time is approved, the observer will be contacted by the NuSTAR Science Operations Center for further details, including observing strategy and other relevant constraints. Proposals deemed infeasible at this stage will be dropped.

---