Suzaku Announcement of Opportunity (AO-9)
Tadayuki Takahashi (Project sub-manager, ISAS/JAXA)
Hideyo Kunieda (Project scientist, Nagoya University)
The X-ray Astronomy satellite Suzaku was developed under the collaboration of Japan and the United States, and was launched by ISAS/JAXA on 2005 July 10. Suzaku has successfully carried out astronomical observations using the X-ray Imaging Spectrometer (XIS) and the Hard X-ray Detector (HXD). After the initial operation for instrument calibration and performance verification, which confirmed the wide-bandpass, high-sensitivity, moderate spectral resolution capabilities of Suzaku, we entered the international AO phase of the mission in 2006 April, performing observations based on proposals received from the astronomical community world-wide. In the meanwhile, however, the amount of electric power supply from the Solar Array Paddle (SAP) has decreased.
The figure shows the yearly profile of the electric power supply with the origin of the ordinate being set at the launch date of Suzaku, 2005 July 10. The numbers at the right end of the panel, arranged vertically, are the numbers of years since launch. The power started to decrease immediately after the beginning of the 7th year (yellow dots), and eventually could not supply enough power to retain full functionality of the spacecraft on 2012 January 24, at which date Suzaku entered into the automatic power reduction mode (so called "Under Voltage Control" mode). After this, for half a year, the power amount reduction seemed to continue, and the project team suspected, at around the end of the 7th year, that even the completion of the AO-7 observations might be impossible. In the early 8th year (orange dots), however, the power reduction seemed to stop. Accordingly, the project team decided to issue AO-8 on 2012 October 1.
As the data of the 8th year are being accumulated, it is found that the reduction of the SAP electric power supply stopped at around the 140th day in the 7th year. After that, the power reduction from the 7th to 8th year is around 50W. The minimal electric power necessary for Suzaku to retain current performance is 800W, which is indicated by the horizontal dashed line at the bottom of the figure. On the other hand, simple extrapolation of the electric power supply history suggests that the minimal electric power during the AO-9 period is probably in the range 850W-900W, and thus it seems, at this moment, possible for Suzaku to survive until the end of the AO-9 period. Accordingly, the Suzaku project team hereby solicits submission of observation proposals for AO-9 starting in 2014 April. But the team would like the proposers to note the following points.
- Although the project team will make their best effort to continue normal Suzaku observations, some of the instruments may be shut down before the end of the AO-9 (2015 March 31). Further crisis of the electric power supply may lead to termination of AO-9 in mid-course.
- Accordingly, the project team solicits proposals whose scientific objectives can be achived within this AO (AO-10 may not be released). The team also welcomes resubmission of past successful proposals under certain conditions. Please refer to section 4-(2) for further details.
- As in AO-8, the project team limits the observable sky to the range 70-110 degrees from the sun. This may lead to a reduction of the number of TOO and time-critical proposals to be accepted (see below for further details).
- We resume solicitation of Key Project proposals, which was suspended
in AO-8. Note, however, that a proposal continuing beyond a single AO
period is prohibited in AO-9; the Key Project proposals solicited this
time should achieve their scientific purpose within the AO-9 period.
The Key Project program was initiated in AO-4, in order to fully utilize the unique capabilities of Suzaku. The Suzaku project team expects to carry out observations that challenge important astrophysical issues and will be utilized for a long time after the observations as a legacy of Suzaku. See the separate announcement for further details.
During the AO-9 period, observations on the basis of the Suzaku-Fermi joint program initiated in AO-6, and the Suzaku-Chandra program initiated in AO-4, will also be carried out. We refer the interested parties to the home pages of Fermi and Chandra, respectively.
This call for proposals is applicable to scientists based in the US.
Scientists in ESA member countries should consult the version at ESA, while scientists in all other countries, including Japan, should consult the version at ISAS/JAXA.
2. The Suzaku Observatory
The Suzaku satellite carries four modules of the X-Ray Telescope (XRT) that focus X-rays up to ~10 keV with high efficiency. An X-ray CCD camera (XIS) module is mounted in the focal plane of each XRT. The XIS has a high sensitivity and moderate spatial resolution, and is particularly suitable for studies of extended sources. The XIS also has a good spectral resolution for soft X-rays below 0.8 keV, which is superior to that of Chandra and XMM-Newton. Moreover, we have applied Spaced-row Charge Injection technique for the XIS since AO-2 to suppress degradation of energy resolution. The HXD has unprecedented sensitivity in a wide energy range up to 600 keV, although it has no imaging capability. The wide bandpass coverage of 0.2 keV through 600 keV with the XIS and the HXD is an important characteristic of the Suzaku mission.
The technical description of the Suzaku instruments and the list of targets that have been observed or accepted can be found through the Suzaku Guest Observer Facility homepage.
3. Mission Phases and Time Allocation
The Suzaku mission has been developed and maintained under collaboration of Japan and the US, and the Scinece Working Group (SWG) that consist of researchers involved in the developement and the operation oversees the project oaverall. Since the end of the SWG phase of the mission (2006 March), all observation time except:
- Observatory Time (3%) for satellite maintenance and related purposes
- Calibration time (5%) for ongoing calibration of the instruments; and
- Director's Discretionary Time (DDT; 5%) for observations of gamma-ray bursts or any genuinely unpredictable events, and other important observations granted at the discretion of the mission director.
The remaining 87% of the total time, which amounts to 360d x 38 ksec/d x 0.87 = 11902 ksec per year, is open to the AO-9 program, and is distributed among Japan, US, ESA and other countries as follows.
|(1)||Japan time||5451 ksec (ESA 909 ksec, Japan and others 4542 ksec)|
|(2)||US time||3963 ksec|
|(3)||Joint Japan-US time||488 ksec|
|(4)||Key project time||2000 ksec|
Here the Japan time includes joint Japan-ESA time, which amounts to 909 ksec. Accordingly, the remaining 4541 ksec is the time for Japanese scientists in AO-9. All proposals from outside Japan, US and ESA should be submitted to the Japan time. Note, however, that the total approved exposure time of proposals whose principal investigators (PIs) are not Japanese nor from ESA member states is not to exceed the joint Japan-ESA time. The joint Japan-US time will be used if proposals for the same targets are accepted both in Japan and US, and if both PIs accept such merging (the proposal form has a check box for the PI to indicate whether he/she accepts the merging). Observation time from Suzaku-Fermi and Chandra-Suzaku joint programs are included in one of the above nationality-based categories, depending on the PI's affiliation. The Key Project time allocation is the same as in AO-7.
4. Proposal Policies
(1) Only researchers based in the US and affiliated with a US institution are eligible to submit their proposals to NASA as the PI. In rare cases, a single PI may be considered eligible to submit Suzaku proposals through multiple agencies. Such a PI must, however, choose a single agency for all his/her AO-9 proposals; it is forbidden for a single PI to submit proposals to multiple agencies during a single cycle, even if they are for independent projects. On the other hand, there can be co-Investigators from any countries in proposals submitted to NASA.
(2) The complete list of targets accepted through AO-8 can be found in the Timeline & Mission Information section of the Suzaku GOF site. The observations of priority A and B targets are guaranteed. New proposals for these targets will not be approved without an explicit justification for an additional observation, such as much longer exposure, different pointing position on the same extended object, or a different phase of a variable object. Given the possibility that AO-9 is the final general call, proposals which are similar to past observation programs are welcome if the new data are expected to strengthen past results. These include, for example, enhancement of statistics of a certain object by simply adding exposure time, completing a mapping observation to cover the entirety of a diffuse object, and increasing the number of samples from a certain source category. In addition, the next generation X-ray observatory ASTRO-H will be launched in the Japanese fisical year 2015. Proposals whose scientific purpose can be extended with ASTRO-H are also welcome.
On the other hand, some of the priority C targets and TOO targets are not observed. This can be checked at this page at ISAS.
Any PI can submit proposals for the C or TOO targets that are unobserved. It must be noted, however, that unobserved AO-8 C or TOO targets may be observed by the end of AO-8 period (March 2014). In this case, the observations of the C targets are regarded as being completed if the exposure time exceeds 70% of the proposed time. If the exposure time is less than 70 %, on the other hand, an additional observation will be carried out to fill the remaining time only if a proposal for the same target from the same PI is accepted at a higher priority (A or B) in AO-9. Otherwise, the observation carried out in AO-8 is ignored, and the target is open for competition in AO-9.
(3) The exposure time of the observation should be justified based on the specific scientific objectives, preferably using simulations. The project team sets the minimum exposure time of a single pointing observation at 10 ksec, considering the observation efficiency. On the other hand, if sufficiently strong justification is provided, long observations can be awarded through the regular proposals (up to 400 ks in Japan and up to 1 Ms in the US). Note that any observations based on a proposal whose approved total observation time exceeds 300 ksec are open to the public as soon as the data are ready for analysis (no proprietary is awarded to the proposer).
(4) A continuous observation of a single target is guaranteed for up to 100 ksec. This limitation originates from the moon light constraint to the star trackers' field of view, conflict with other time critical observations, and other operational/planning difficulty. The operation team accepts requests for uninterrupted observations longer than 100 ksec, but these will be carried out on a best-effort basis.
(5) Target of opportunity (TOO) proposals are allowed for short-lived events on known objects whose timing is uncertain. This category is referred to as "Reserved TOO observation.". In this case, the condition to trigger the observation, the estimated probability of the event to take place during the AO-9 period, and the expected duration of the event should be specified in the proposal, as well as other information required for non-TOO observation proposals. Any proposal that does not name a specific target, such as "Observation of a forthcoming nearby supernova," or "next nova explosion in M31," will not be accepted. The number of potential targets for a TOO proposal is limited to at most 5 per proposal. The scientific justification of TOO proposals must specify how many targets should be observed (the number of "triggers") to fulfill the scientific goals of the proposal. If the total exposure time to complete the requested number of targets is equal to or larger than 300 ksec, the data will be open to public as soon as the first observation is finished. See (3) above.
(6) It is possible to submit proposals specifying the time of observations as TC (Time Critical) observations. These include observations of a specific binary phase, coordinated observations with other wavebands, monitoring a target several times with certain time intervals, roll-angle-constrained observation of diffuse sources, and so on. Multi-pointing observations of a variable target (even with no other constraints, such as "3 separate observations any time during the AO-9 period") are also considered TC. So is a background observation to be carried out close to the time of the main target observation. The Suzaku operation team will do their best to perform the observations as requested. In all these cases, the PI must check the TC flag in the target form. Even if the coordination with other instruments is not planned in detail at the time of the proposal submission, the PI is required to check the TC box if he/she would like to do so after the approval of the proposal. The observation without a TC flag is treated as non-TC observation, and the coordinated observation can only be carried out if the other telescopes follow the Suzaku schedule.
(7) Any genuinely unpredictable events, such as gamma-ray bursts and supernovae, can be observed as part of the DDT ("realtime TOO observation"). Proposals for realtime TOO observations are accepted at any time outside the selection process of ordinary proposals. See this ISAS page for further details. There are no proprietary data rights for realtime TOO observations. Note that real-time TOO proposals for gamma-ray bursts can be accepted from any investigators starting in AO-7.
(8) The Suzaku project will accept proposals using P-sum/timing mode for the XIS, as well as the normal imaging mode. In the P-sum/timing mode, photon pile-up is unimportant, and a time resolution as fast as 7.8 msec can be achieved, although only 1-dimentional images can be obtained. Note, however, that the P-sum/timing mode can be used only for XIS3, and neither Spaced-row Charge Injection nor CTI correction can be applied, and hence the energy resolution is significantly worse than in the normal imaging mode. In addition, the calibration accuracy is not as good as in the normal imaging mode. Refer to the technical description document for details on the P-sum/timing mode.
(9) The project team has supported two default aim points since AO-1: the XIS nominal and the HXD nominal positions. Of them, the team ceased to support the HXD nominal poisition as of AO-7. As a result, the standard response matrices will not be provided for the HXD nominal pointing. No observations with non-standard readout clocks (P-sum/timing mode and window/burst options) will be carried out at the HXD nominal position. Note, however, that the operation team does not prohibit observations at the HXD nominal point with a standard XIS mode, at the proposers' own risk.
(10) We resume the solicitation of Key Project proposals in this AO. See the separate document for further details.
5. Review Process and Schedule
Researchers based in the US and affiliated with a US institution should submit their proposals to NASA. The deadline is 2013 November 13 at 4:30 pm EST for proposals submitted to NASA. After the US national review, a Japan-US merging committee will be convened in late February, 2014, and the final observing program will be published soon thereafter.
Accepted targets will be classified into three categories (A, B, and C) based on proposal ranking. Priority A targets will be preferentially observed during the AO-9 period (2014 Apr to 2015 Mar), and the observation are regarded as completed if the exposure time is more than 90% of the requested time. Priority B targets will be scheduled in this period as much as possible, but may be carried over to the next cycle. Observations of the priority B targets are regarded as completed if the observation covers more than 70% of the requested time. Priority C targets will be used as fillers when there are gaps in the schedule. Of the total available time T (=11902 ksec = 360 d x 38 ksec/d x 0.87), we will accept 0.6T (=7141 ksec), 0.3T (=3571 ksec) and 0.5T (=5951 ksec) for Key+A, B, and C proposals. This implies an oversubscription fraction of 40%. Oversubscribed targets will be scheduled if observing time remains after the observatory time, the calibration time, and DDT are assigned.
Reserved TOOs and time critical observations pose constraints on Suzaku operation. Hence the total fraction of them is limited to be some 15% of the total available time. Note that we will review this fraction at the time of the merging committee meeting (mid February 2014), based on the up-to-date prospect of the SAP power supply degradation information.
6. Data Rights
Normally, proposers of regular proposals have proprietary rights to the data for 1 year after receipt of the processed data. This does not apply to the data based on the proposals whose total exposure time (including those for priority C targets) is equal to or more than 300 ksec.
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