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Following the PV phase, XRISM has entered the Guest Observer (GO) phase, in which it will remain for the lifetime of the mission, with Announcements of Opportunity (AOs) released simultaneously by JAXA, NASA, and ESA (Hayashi et al., 2025). Cycle 3 will cover a 1-year period, starting on or about June 1, 2026, and therefore ending on or around May 31, 2027. The institutional affiliation of the principal investigator determines the agency to which they should propose. Persons at Japanese institutions should submit to the JAXA solicitation; those at US or Canadian institutions should submit to the NASA solicitation; and those with affiliations in ESA member countries and cooperating states should submit to the ESA solicitation. Persons with affiliations outside Japan, the US, Canada, or an ESA member state should submit to the JAXA solicitation, which reserves some time for such international proposals.
Proposers must provide all information that is indispensable for operation planning on the electronic forms. Proposers with detailed requests that cannot be expressed with the check boxes/pull-down menus are advised to utilize the “Remarks” area. It is the PI's responsibility to ensure that all information entered into the forms are accurate, even though some checks will be performed during the course of the proposal review and observation planning. This includes the target coordinates: positional accuracy of better than 1 arcmin is required, and a higher accuracy is recommended. Note that there have been cases where blind reliance on coordinate resolvers such as SIMBAD resulted in incorrect target coordinates.
The details of the proposal calls are described more fully in the Announcement of Opportunity (AO) documents issued by the three agencies. As with previous missions, proposals will be received by the relevant agency and evaluated by subject matter experts organized into review panels that make up the Time Allocation Committee.
Accepted targets will be classified into three priority categories: A, B, or C. Priority A and B targets are guaranteed to be observed, with A targets receiving a higher priority for observation scheduling. Priority C targets will be used as fillers when there are gaps in the schedule. Priority A and B targets that have not been completed by the end of an observing cycle are carried over into the next cycle (see below for exceptions to this rule). Priority C observations that are not observed during that observing cycle are not carried over. The goal of the target selection process is to produce a combined list of targets representing approximately 140 percent of the available observing time, split among A (50 percent), B (40 percent) and C (50 percent) priority observations.
Category A and B targets will be considered complete if 90% (for A targets) or 70% (for B targets) of the proposed time is obtained on the source. In general, supplementary observations will be performed for A or B targets that do not meet the completion criteria, although it may not always be possible in case of time critical observations.
No multi-cycle proposals are solicited. That is, proposals that require observation beyond the Cycle 3 period will not be accepted.
TOO proposals are allowed for XRISM through the normal AO process, although they must be ranked as Priority A to be accepted, and limited to 10% of total available time. Proposals with TOOs should not be mixed with non-TOO targets. TOO proposals are allowed for short-lived events in known objects, the timing of which is uncertain. The trigger criteria must be explicit and quantifiable, and stated in detail in the proposal text; a brief summary including the trigger criteria and relevant quantities should be clearly provided in the “Remarks” section of the target form. In addition, TOO proposals must provide an estimated probability of a successful trigger during the AO period. Generic TOO proposals without a specific target (such as “a nearby supernova”) will not be accepted through the AO process. In the same split, the number of targets in TOO proposals should not exceed 10.
It is the PI's responsibility to notify the XRISM project when the criteria are met, via https://xrism.isas.jaxa.jp/research/proposer/too/index.html.
Even though TOO targets must be Category A to be accepted, untriggered TOO observations will not automatically be carried over to subsequent cycles.
Proposals for observations with scheduling constraints imposed either by the nature of the target or the requirement for coordination with other ground- or space-based observatories are allowed. These are classified as time-critical (TC) targets. There is no prohibition on mixing TC and non-TC targets within a single proposal.
Coordinated observations with other observatories are considered TC, regardless of whether the timing of observations with other observatories are known in advance or not. This also applies to the case when the observing time on the other observatory (or observatories) have not been secured at the time of submission of XRISM proposal, since if coordination is essential, we cannot guarantee coordinated observations if a target is not labeled TC, (see also Section 3.4). Observations during a specific binary phase is another category of TC targets. If a specific roll angle is required, that is also considered TC. Monitoring observations (repeat observations of a target at some desired time interval) are also classified as TC. Finally, we have a catch-all category of “specific date” in case the nature of the scheduling constraint does not neatly fit into the pre-defined categories.
TC targets must be classified as priority A or B to be accepted. In addition, there is a cap of 20% as the total time of TOO and TC observations (of which only up to 10% can be TOOs, as stated in Section 3.2).
It is the PI's responsibility to ensure that the proposed time constraint can be met during the Cycle 3 period. Mission operation team will prioritize scheduling of TC targets over that of other priority A and B targets. If, nevertheless, a TC targets cannot be observed during the Cycle 3 period, the general policy is for them to be carried over to Cycle 4. However, there may be cases where the nature of the time constraint is such that this is not practical. The fate of any such observations will be determined on a case-by-case basis.
In Cycle 3, proposer can request XRISM observations jointly with XMM-Newton and/or NuSTAR. Such proposals must provide a compelling justification for the need for joint observations. Proposers have the option of also describing scientific objectives that are achievable with XRISM time alone. Depending on the strengths on both these elements (among others), the XRISM project may approve joint observations, reject the Cycle 3 proposal altogether, or approve only the XRISM observations; however, the XRISM project cannot approve XMM-Newton and/or NuSTAR observing time when the XRISM time is not approved. Joint proposals are not necessarily simultaneous or coordinated between facilities, although many are expected to be. Any such constraints (or a lack thereof) must be separately specified and justified in the observing proposal.
Joint TOO proposals are allowed. If requesting simultaneous TOO observations, proposers must note the observatory with the slower (or slowest) response time, and demonstrate that it is adequate to achieve their scientific objectives. Also, it is the PI's responsibility to notify both (or all) observatories if such a proposal is accepted and the triggering criteria are met.
Up to 200 ks of XMM-Newton time will be available to XRISM observers in Cycle 3. Proposals for joint XRISM-XMM-Newton observation must include the choice of prime XMM-Newton instrument, the requested XMM-Newton exposure time, and information on any scheduling constraint. The rationale for the proposed XMM-Newton exposure time must be described in the proposal with sufficient details.
Establishing technical feasibility is the responsibility of the proposer, who should review the relevant XMM-Newton documentations. All standard observing restrictions apply to joint proposals. For proposals that are approved, the XMM-Newton project will perform detailed feasibility checks and 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.
Up to 500 ks of NuSTAR time will be available to XRISM observers in Cycle 3. A technical description of NuSTAR, and considerations important for proposers can be found at NuSTAR proposal page (https://heasarc.gsfc.nasa.gov/docs/nustar/nustar_prop.html)
and the NuSTAR Science Operation Center page
(https://nustarsoc.caltech.edu/NuSTAR_Public/NuSTAROperationSite/Home.php)
Proposals for joint XRISM-NuSTAR observations must include the total requested NuSTAR observing time, the expected NuSTAR count rate, and an evaluation of possible stray light contamination.
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.
Proposals for observations of targets that have been previously observed in any phase of the mission are permitted. However, such proposals must demonstrate the need for additional observations of the target, e.g., observations during a different binary phase or source state, observation of different locations within extended sources, or observations with a significantly higher statistical quality. This policy also applies to approved Cycle 2 Priority A or B targets that have not yet been observed, since their observations are guaranteed. TOO targets are an exception to this rule, however, since they will not be carried over to Cycle 3 period. Proposals on unobserved TOO targets and unobserved Priority C targets can be written under the assumption that the approved Cycle 2 observations will not take place, and be submitted by any group. Such proposals may be accepted conditionally, depending on whether the approved Cycle 2 observations actually take place or not.
Commissioning and calibration observations may or may not be scientifically usable due to a variety of factors including special instrument configurations. Such observations can be identified by the first digit of the 9-digit observation number known as obsid. If the first digit of obsid is 0, then it is a commissioning observation; if it is 1, it is a calibration observation. Those who are interested in scientific observations of commissioning or calibration targets are encouraged to contact the helpdesk, so that they can learn the instrumental configuration and any other relevant factors and make an informed choice regarding a potential proposal. The same set of information will be used in the review process to determine if the proposed observation constitutes a duplication or not.
Similarly, proposers may request multiple observations of the same target for a specific investigation. However, such requests will be approved only if a clear scientific and logistical justification of the need for separate observations is provided in the proposal.
The solar panels on the XRISM satellite are fixed. This places a restriction on the pointing direction with respect to the satellite-Sun line: the Sun angle constraint during Cycle 3 is 60–120 degrees. This means that at any given time of the year, only a swath of the sky 60 degrees wide is accessible for astronomical observations, and thus most celestial sources are available for observations for about 60 days every 6 months. If a specific observing date or a coordinated observation with other missions is required, the proposer must first determine if the observation is possible. This can be done using the “Viewing” tool on the HEASARC website (https://heasarc.gsfc.nasa.gov/cgi-bin/Tools/viewing/viewing.pl).
Long (
1 day) observations are the norm for XRISM. A large number of short observations is an inefficient use of the satellite because of the unusable time during slews and attitude settling. The pointing is expected to be accurate to 0.2
and can be reconstructed to better than 0.1, excluding the first 2 orbits (Kanemaru et al., 2025). Moreover, there is a limit on the number of slews that can be uploaded to the XRISM satellite. For these reasons, a minimum exposure time of 10 ks has been set for all proposed observations. For Cycle 3, observations will be limited to 500 ks per pointing with the total not to exceed 1 Ms per proposal.
Contiguous observations, i.e., observations not disrupted by the observation of another target, are the norm. However, it is possible that some long observations may be scheduled in several blocks; if an uninterrupted observation is essential for the scientific objective, this should be noted in the proposal.
Even during “contiguous” observations, there will typically be interruptions due to the location of XRISM in a low Earth orbit: Normally, a target will be occulted by the Earth for 
30 minutes every satellite orbit (96 min). In addition, XRISM will pass through the South Atlantic Anomaly (SAA) during parts of 5 or 6 orbits every day. Due to the harsh radiation environment of the SAA, scientific observation is not possible during SAA passages.
There are also constraints on the orientation of the projected Resolve and Xtend FOV on the sky. Since both are approximately square, specific roll angle is not expected to be a common requirement. However, if a specific roll angle is scientifically advantageous, the proposer must first determine if it is feasible, using the XRISM Roll Angle tool available via the GOF website. If feasible, the required roll range can be entered on the proposal form. For objects close to the ecliptic poles it is possible to arrange for any roll angle by scheduling observations at a specific time, but for those located close to the ecliptic plane, Resolve and Xtend will project on the sky in a nearly fixed orientation. Note that any roll constraint will make a proposal time critical.
Observations of some Solar System objects are possible, but others are not. The allowed Sun angle range precludes observations of Mercury or Venus. The Moon is another object that cannot be observed with XRISM, in this case because the star trackers cannot be used when the Moon is in their fields of view. While the pointing directions of the star trackers are offset from that of the X-ray instruments by 10 degrees, this offset is small compared to the fields of view of the star trackers, thus making it impossible to observe the Moon.
XRISM observations of objects in the outer Solar System is possible by making many small maneuvers (XRISM only performs observations of fixed celestial coordinates at any given time). However, maneuvers may only be performed every 2 orbits. If the Solar System object is moving slowly, or if the X-ray emitting region has a large (compared to XRISM FOV) angular extent, then this strategy may enable useful observation to be performed.
After the XRISM proposal deadline, there will be three independent proposal reviews for the NASA, JAXA, and ESA proposal solicitations. Each review will create a target list from the proposed observations, ranking the accepted targets as category A, B, or C. Only category A and B targets are guaranteed to be observed.
Category C targets will be observed as time permits. An international merging committee will collate the three target lists and produce a single, unified list. Overlaps among targets accepted by multiple agencies will be resolved, either by merging the investigations (if both parties are willing) or by choosing one. In the latter process, the priority given by the national reviews, as well as the lengths of the accepted observations, will be considered. The final target list will be 40% oversubscribed. Category A targets will have 50% of the available time, category B 40%, and category C 50%.
The Cycle 3 allocation of GO time among the mission partners is 48% for Japanese investigations (including 4% for international proposals), 44% for US investigations (including Canada), and 8% for ESA investigations.
Even though observations are scheduled to acquire roughly the approved exposure time and although this will usually be achieved with XRISM, occasional losses of usable observation time are inevitable. As mentioned above, Category A observations will be deemed complete when they have received at least 90% of the approved time. Note that this will be judged based on the good time intervals of the cleaned Resolve event files after the standard screening. Additional observations will be scheduled automatically for those non-time-critical targets the observations of which are considered incomplete by the project scientist at ISAS. In the case of time-critical observations which are incomplete or unusable, it will be the PI's responsibility to determine the best course of action.
Each PI will be assigned a contact duty scientist who will work with the PI to assure the maximum science return. This will include double-checking coordinates, count rates and finalizing configurations (nominal pointing, modes, etc.). It is important to note that once an observation has been scheduled, any delay in responding to questions from the contact scientist may result in targets being removed from the schedule.
Once the observation has been completed, the data will be promptly run through the processing pipeline and put into both the US and Japanese archives in encrypted form. The PI will be sent the decryption key, along with instructions on how to download and decrypt the data.
With the exception of the code that converts raw binary telemetry into FITS format files (Eguchi et al., 2025), all XRISM software is written as FTOOLS and distributed through the XRISM team at ISAS/JAXA and the NASA/GSFC HEASARC. This includes the tools used in the processing. All calibration files are distributed through the HEASARC caldb (calibration database) system. This enables users to apply any calibration updates themselves. The XRISM team at ISAS and the NASA XRISM GOF provide additional FTOOLS that may be necessary or desirable for analyzing XRISM data. The use of other software packages will only be supported at a lower priority level.
While Cycle 3 and subsequent AOs for XRISM proposals represent the main venue to request XRISM observations, there are others.
The AO process restrict TOO proposals to unpredictable events of known objects. For transient events of a previously unknown target (such as “a nearby supernova”), real-time TOO requests can be submitted through
https://xrism.isas.jaxa.jp/research/proposer/too/index.html
(the same web page as used for triggering pre-approved TOO observations).
In addition, the XRISM project has made arrangements with several observatories, allowing proposers to request joint XRISM time through their proposal calls. The recent and current such opportunities are Swift Cycle 22, IXPE Cycle 3, XMM-Newton AO-25, and NuSTAR Cycle 12. While these arrangements are likely to continue for future proposal calls, the details are subject to discussion and agreement between XRISM and these missions.
The data rights policy for XRISM is similar to previous JAXA-led X-ray astronomy missions. The normal exclusive use period for GO data secured through the AO process is one year after the delivery of pipeline-processed data. On the other hand, data from calibration observations and real-time TOOs (i.e., those requested outside the AO process) will not have any exclusive use period.
We make a slight distinction between Resolve and Xtend data in this regard. One is for the purpose of XRISM Xtend transient search (XTS; see the results page at https://xrism.isas.jaxa.jp/research/about/XTS/index.html and Tsuboi et al. 2025). With the advanced permission of the proposers, the XTS team will search for any transients within the Xtend field-of-view (FOV) but outside the Resolve FOV. If one is found, it will be quickly reported as an Astronomer's Telegram or on General Coordinate Network (GCN) with the proposal PI listed as a co-author, if desired, but without consultation regarding its content.
The other is regarding any real-time TOO requests that overlap with FOV of the accepted proposals. A real-time TOO request will not be accepted if the requested Resolve FOV overlaps with that of an approved observation. This is because data resulting from real-time TOO requests are immediately public. However, this policy does not preclude a real-time TOO observation whose Resolve FOV falls within the Xtend FOV (but outside the Resolve FOV) of an approved observation.