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4. Observation Policies

In AO-10, 100% of the observing time available is used for GO observations. The current schedule for the time allocation between Japanese and US PIs is given in Table 4.1. The AO will run for a six month period starting in May 2015.

Over the past several years, we have seen a decline in the electric power supply from the Solar Array Paddle (SAP) as well as the capacity of the on-board batteries. It is now rare to be able to operate both XIS and HXD simultaneously. Based on a careful monitoring of the power situation, the project has decided to proceed with the 10th announcement of opportunity (AO-10), but with several notable changes since AO-9.

After years of operation, we know that the actual observing efficiency is about 38ks per day and we assume 180days of operations during the AO-10 period. From the total of 6840ks, we subtract 3% of the available time as observatory time used for satellite maintenance and similar purposes, and 5% for ongoing calibration observations. Finally, 5% are earmarked as Director's Discretionary Time (DDT) for unproposed Target of Opportunity (TOO) proposals (including observations of gamma-ray bursts) and other important observations, granted at the mission director's discretion. Therefore $6840\times0.87=5951$ks are nominally available to the community via the proposal selection process.

The project will over-subscribe this total by 40% including category C targets for which the observation is not guaranteed (see Section 4.4 below). If the actual sum of the observatory, calibration, and director's times is less than 13%, additional C targets will be observed.

In this AO, 2,975ks are assigned to Japanese observations and 2,332ks go to US observations. The remaining 744ks are set aside for joint Japan-US investigations. When the respective national reviews have selected the same target, the two proposals will be merged if both teams indicated their willingness to collaborate on the RPS form, and the observation will be counted against the Japan-US time. If such mergers do not take up 744ks, the remainder will be divided between separate Japanese and US investigations. Additionally, within the "Japanese" allocation, 476ks are reserved for proposals submitted to ESA as joint Japan-ESA observations. Proposals from non-US, non-ESA countries will be accepted within the Japanese time up to the ESA portion.

Table 4.1: Suzaku time allocated to each group of observers. The ESA time is in parentheses as it is part of the Japanese allotment.

Phase Months Post-Launch SWG Japan (ESA) US Japan/US Key Project
AO-9 118-123 0 2975 (476) 2332 744 0

In this AO, the scientific justification must address the following in case the number of XIS units in operation is reduced. First, the exposure time of each observation will be increased according to the number of available XIS modules by default. The proposer should evaluate the effect of this in achieving their scientific objectives. For example, a time critical observation of a short-lived event may suffer if the total exposure time is tripled but with only 1 XIS in operation. In addtion, while 3 XIS units are in use, proposers who whish to obtain P-sum/timing mode data would also obtain normal imaging mode data. The proposer should address their preference if only 1 XIS unit is available.

The nationality of the PI's institution determines which agency should receive the proposal. That is, researchers at US institutions must submit their proposals to NASA and those at institutions in ESA member countries must submit theirs to ESA (regardless of their actual nationality). While the ISAS/JAXA proposal process is primarily aimed at researchers resident in Japan, proposals from researchers in other (non-US, non-ESA) countries will also be considered. A PI with dual affiliations generally must choose a single agency for all his/her AO-10 proposals, even if they are for independent projects. Only in rare cases, a single PI may be considered eligible to submit Suzaku proposals through multiple agencies. Co-Is from any country may be part of any proposal, though.

Regular US proposals may request no more than 1Ms of observing time for practical reasons (there is no formal upper limit for ISAS/JAXA proposals). Note that for TOO proposals this 1Ms limit applies to the actually requested observing time. It is therefore possible to request 400ks per target for up to 2 triggers among 5 potential targets, for example.

4.1 Data Rights

The data rights policy for Suzaku is similar to previous missions. The normal exclusive period for GO data is one year, except for proposals with a total requested exposure time $>300$ks (including priority C targets), and DDT data which are made public immediately.

Accepted targets will be classified into three categories. Priority A targets will be preferentially observed during the AO-10 period (May 2015 to October 2015). Priority B targets will be scheduled in this period as much as possible, but may be carried over to the next cycle. Priority C targets will be used as fillers when there are gaps in the schedule. For the total available time T, we currently plan to accept 0.6T, 0.3T, and 0.5T as As, Bs, and Cs (for a total over-subscription by 40%).

During AO-10, 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.

During the GO phase, data from calibration and TOOs requested outside the proposal process (see below) will not be considered proprietary.

4.2 Target of Opportunity Proposals

TOO proposals are allowed for Suzaku through the normal proposal process, although they must be highly ranked (see below) to be accepted. 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 should appear 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. It is the PI's responsibility to notify the Suzaku project when the criteria are met. Generic TOOs without a specific target (such as "a nearby supernova") will not be accepted. In the same spirit, the number of targets in TOO proposals should not exceed 5. Gamma-ray bursts or any genuinely unpredictable events may be observed outside the proposal process, as part of the 5% DDT. Data from such observations will not have a proprietary period.
To request such unproposed TOO observations, please send an e-mail to: suzaku_managers $<$at$>$ using the format specified in

4.3 Pointing Constraints

The Solar panels on the Suzaku satellite are fixed. This places a restriction on the pointing direction with respect to the satellite-Sun line: the Sun angle constraint during AO-10 is 70-110degrees. This means that at any given time of the year, only a swath of the sky 40degrees wide is accessible for astronomical observations, and thus most celestial sources are available for observations for about 40days every 6months. 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 Suzaku proposal web-site (see Appendix B).

Long ($>$1day) observations are the norm for Suzaku. 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 0.3arcmin and can be reconstructed to better than 0.2arcmin, except during the initial settling period of up to 10minutes. Moreover, there is a limit on the number of slews that can be uploaded to Suzaku. For these reasons, a minimum exposure time of 10ks has been set for all proposed observations.

Contiguous observations, i.e., observations not disrupted by the observation of another target, are generally guaranteed up to exposures of not more than 100ks. This limitation is due to moon light constraints for the star trackers' field of view, conflicts with other time critical observations, and other operational/planning difficulties. While the operation team does accept requests for uninterrupted observations longer than the 100ks, these are conducted on a best-effort basis.

Even during shorter pointed observations, there will typically be interruptions due to the location of Suzaku in a low Earth orbit: Normally, a target will be occulted by the Earth for $\sim$30minutes every satellite orbit. In addition, Suzaku will pass through the South Atlantic Anomaly (SAA) during parts of 5 or 6orbits every day. Due to the harsh radiation environment of the SAA, scientific observation is not possible during SAA passages. There are other variations in the particle background, depending primarily on the Cut-Off Rigidity (COR)4.1. Please check the Suzaku web-sites (see Appendix B) for the most up-to-date suggestions to reduce times of high background while maximizing the science.

There are also orbital constraints on the orientation of the projection of the XIS CCDs on the sky. Since the Suzaku XIS arrays are square, with calibration sources in different corners, selecting a specific roll angle is rarely significant. However, if a specific roll angle is scientifically advantageous, the proposer must first determine if it is allowed. This can be done using the MAKI tool or the alternative rollRange tool described in Section 5.7. Then the required roll range can be entered on the RPS proposal form. For objects close to the ecliptic poles it is possible to arrange for any XIS orientation by scheduling observations at a specific time, but for those located close to the ecliptic, the XIS will project on the sky in a nearly fixed orientation. Note that any roll constraint will make a proposal time critical.

It is possible to specify the time of observations (time critical, or TC, observations) in order to observe during specific phases or for simultaneous observations. Monitoring observations (repeated observations with a specified interval) or roll-angle constrained observations are also considered time critical, and must be so flagged on the proposal form. The total accepted time of TC and TOO proposals is less than 15% of the total observation, and proposers should justify their requirements carefully.

Overall the proposers are strongly urged to provide accurate information. All information that is indispensable for operation planning should be provided on the electronic forms. The PIs are advised to utilize the ``Remarks'' area if they have detailed requests which cannot be expressed with the check boxes/pull-down menus.

4.4 Events After Submission

After the Suzaku proposal deadline, there will be three independent proposal reviews for the US, Japan, and ESA proposals. 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. As stated above, TOOs and time critical observations are only accepted within 15% of the total time - however, the project will review this limit given the most up-to-date status of the electric power supply status at the time of the international merging meeting in April 2015. 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 between US and Japanese targets 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 $\sim
40$% oversubscribed. Category A targets will have 60% of the available time, category B 30%, and category C 50%.

Even though observations are scheduled to acquire roughly the approved exposure time and although this is usually achieved with Suzaku, 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 XIS event files after the standard screening. Dead times (including those due to the use of the burst option) are not taken into account. Also, the standard screening for the HXD is more strict, so the effective exposure for the HXD is often smaller than that of the XIS by 20% or more. 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.

As mentioned above, should the power supply situation deteriorate further, the number of XIS units in operation may be reduced from 3 to 1. In this case, the exposure times of accepted observations will be multiplied by 3 by default.

Each PI will be assigned a contact scientist, either at ISAS or the NASA Suzaku GOF, 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, XIS modes, ...). 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. We do not have a mechanism to approve coordinated observations with Suzaku and another observatory through a single proposal except for the joint Fermi-Suzaku and NuSTAR-Suzaku programs (please refer to the Fermi and NuSTAR announcements of opportunity for more details). It is the PI's responsibility to secure observing time with other observatories, when simultaneous observations are desirable. Please note that the Suzaku component of such a proposal may be approved contingent on the success of other proposals. Special scheduling requests and TOOs will be accommodated on a best effort basis. For simultaneous observations, the mission scheduler at ISAS, in consultation with the contact scientist, will contact the PI in advance for detailed scheduling information, and will often work directly with schedulers of other missions. During the AO-1-AO-9 observing periods, the Suzaku scheduling team made every effort to accommodate requests of coordinated/simultaneous observations with other facilities and we expect that it will continue to do so during AO-10.

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, initially in encrypted form, unless the proposal has a total exposure time $>300$ks as noted above. The PI will be sent the decryption key, if applicable, along with instructions on how to download and decrypt the data. Another exception to the one year exclusive period for GO data concerns the HXD Wide-band All-sky Monitor (WAM) data (see Chapter 8). The WAM is primarily used for anticoincidence shielding in the HXD, but it can also be used as an all-sky monitor, detecting solar flares, gamma-ray bursts, and other bright X-ray sources (e.g., Cyg X-1). All data from the WAM will be monitored by the HXD team, which will alert the GRB community to any detected bursts. In addition, the HXD team will make analysis results from WAM, such as light curves and fluences, available to the public as soon as possible. These may be used to put limits on GRBs or other events triggered by other satellites or observatories. However, the PI will receive the complete WAM data from their observation and will share data rights with the Suzaku team for the normal 1year proprietary period. This unusual arrangement is due to the time-critical and non-source-specific nature of the WAM data.

With the exception of the code that converts raw binary telemetry into FITS format files, all Suzaku software is written as FTOOLS and distributed through the Suzaku 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 Suzaku team at ISAS and the NASA Suzaku GOF provide additional FTOOLS that may be necessary or desirable for analyzing Suzaku data. The use of other software packages will only be supported at a lower priority level.

next up previous contents
Next: 5. Writing A Successful Up: Suzaku Technical Description Previous: 3. Mission Description   Contents
Katja Pottschmidt 2015-01-27