2. Changes Since AO-9

This chapter summarizes the main changes to the Suzaku Technical Description since the last AO and re-emphasizes several important issues to consider for the preparation of proposals.

New:

1. Over the past several years, we have seen a decline in the electric power supply from the Solar Array Paddle as well as the capacity of the on-board batteries. All new AO-10 proposals should stand on their own merits, in the sense of not requiring future (AO-11) Suzaku observations.

2. The period of AO-10 observations will be 6 months from 2015 May 1 to October 31. The total time nominally available for observations to the community is 6,051ks in AO-10. 2,975ks are assigned to Japanese observations, this includes 476ks for proposals submitted to ESA as joint Japan-ESA observations, and 2,332ks go to US observations. The remaining 744ks are foreseen for joint Japan-US investigations.

3. No proposals that require the use of HXD to achieve their core scientific objectives will be accepted. However, proposals that can be enhanced if HXD is also operated are acceptable.

4. Should the power situation further degrade, the number of XIS units in operation may be reduced from 3 to 1. If this is done, the exposure times of accepted observations will be increased by a factor of 3. Proposers should evaluate the effect on 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 addition, proposers who whish to obtain P-sum/timing mode data would also obtain normal imaging mode data with 3 XIS units in use but should address their preference for the case that only 1 XIS unit is available.

5. This opportunity is for regular proposals only; no Key Project proposals are being solicited or will be accepted.

6. Since some time between 2014-05-15 and 2014-06-02 the charge leakage area on XIS0 expanded. The area discrmination region has therefore been increased from ACTX=70-110 to ACTX=0-210 since 2014-10-01.

Reminders:

1. It is conceivable that the amount of time available for target-of-opportunity and time critical observations will have to be reduced.

2. Before AO-8, targets with Sun angles in a range of 65 to 110 degrees were accessible for Suzaku observations. Considering the power situation, the Sun angle range has been restricted to 70-110 degrees since AO-8.

3. Since the current version of the roll angle tool Maki, which can determine the orientation of the XIS CCDs on the sky as a function of the observation epoch within the visibility window of a target, does not work on 64-bit machines, we provide a simpler, text-only, perl script, RollRange, as an alternative to Maki. See section 5.7.

4. The category of ``Long Program'' for proposals with a total exposure time $>$300ks, available in (only) the US from AO-3 to AO-6 has not been offered since AO-7 anymore.

5. As before all projects with a total exposure time request equal to or more than 300ks are open to the public immediately.

6. Regular US proposals may request no more than 1Ms of observing time for practical reason. 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.

7. Since AO-5, individual raster scan observations have to have the same minimum exposure time of 10ks per pointing as other observations.

8. XIS1 suffered a micro-meteorite hit in December 2009. Following diagnostic measurements showed that the scientific impact is minimal. See section 7.3.6 for more information about other putative micrometeorite hits and their effects.

9. The use of the HXD nominal aim point is discouraged. To this end the HXD team will no longer provide response matrices for simulation for observations at the HXD nominal aim point. The XIS team will no longer support observations at the HXD nominal aim point that use the P-sum mode, the Window option or the Burst option.

10. Two Suzaku memos provide information about the jitter of the pointing direction that can affect observations since the end of 2009
    ( ftp://heasarc.gsfc.nasa.gov/suzaku/doc/general/suzakumemo-2010-05.pdf and
    ftp://heasarc.gsfc.nasa.gov/suzaku/doc/general/suzakumemo-2010-06.pdf).
    Note that the first one describes an effect - the observed light curves being modulated due to telescope vignetting - that is mitigated by not using the HXD aim point. On June 25, 2012, another change has been made leading to the attitude control being good to 1arcmin or better and the attitude determination being good to 20arcsec or better, i.e., back to the original situation. However, the actual behavior differs from observation to observation and the effects discussed above might still occur.

11. Proposals using the P-sum/Timing mode of the XIS are encouraged. There is no longer a limit on the amount of P-sum/Timing mode observations that can be accepted. Proposers should be aware of the properties of the P-sum/Timing mode. Photon pile-up scarcely occurs in this mode, and a time resolution as fast as 7.8ms can be achieved, but only a 1-dimensional image can be obtained. Note that the P-sum/Timing mode can be adopted only for the XIS3, and neither the Spaced-row Charge Injection nor a CTI correction can be applied. The energy resolution is therefore significantly worse than in the normal imaging mode. The calibration accuracy is not as good as that for the normal imaging mode, either.

12. XIS recipes for P-sum data reduction and pile-up detection have been released which are useful for planning observations requiring high time resolution and pile-up mitigation. Please see http://www.astro.isas.jaxa.jp/suzaku/analysis/xis/.

13. For feasibility studies of HXD data analyses proposers should simulate observations with the responses and background files provided for the XIS aim point, then analyze them by varying the background by typically $\pm3$% for the PIN and $\pm1.5$% for the GSO. This procedure mimics the level of systematic uncertainties in the current HXD background models (see sections 5.5.2 and 8.5). The background files were generated based on the Lockman hole observation performed on 2009-06-12. The PIN threshold of Epoch 9 has been applied. Channels below 15keV should be ignored due to uncertainties in the response and background. As long as this is done, simulations based on these files are suitable for simulating AO-10 observations. Keep in mind, however, that no proposals that require the use of HXD to achieve their core scientific objectives will be accepted in AO-10.

14. Note that the Suzaku project has an agreement with the Fermi project as well as with the NuSTAR project to make a modest amount of Suzaku time available for allocation through their proposal review processes for investigations that take advantage of joint observations. See Chandra and Fermi calls for proposals for further details.

15. Real-time TOO proposals (outside the AO process, through
    http://www.astro.isas.jaxa.jp/suzaku/planning/gtoo/) for gamma-ray bursts can be submitted by all investigators, including those who are not part of the Suzaku science working group.