2. Changes Since AO-4

This page 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. Please note that this should not prevent the user to carefully read the new version of the guide as most of the numbers for simulations purposes have changed. These changes are not included here because they are part of the "standard" update of the guide.

1. The total time nominally available for observations to the community is again 11902ks in AO-5 (11902ks in AO-4, 12038ks in AO-3, 11722ks in AO-2). In this AO, 2Ms will again be assigned for Key Projects (see next item), 5451ks are assigned to Japanese observations, this includes 909ks for proposals submitted to ESA as joint Japan-ESA observations, and 3963ks go to US observations. The remaining 488ks are foreseen for joint Japan-US investigations.
2. The new proposal category of Key Projects (introduced in AO-4) will be maintained. These are comprehensive observing programs sampling a number of objects of a particular class, or surveying a large region of the sky, in order to take maximal advantage of the unique attributes of Suzaku to address important astrophysical problems. See http://heasarc.gsfc.nasa.gov/docs/suzaku/prop_tools/keyp5.html for additional information on this new category.
3. In the US, the category of Long Programs (introduced in AO-3) will be maintained, for proposals with total exposure times $>$300ks, encouraging, e.g., long exposures of single objects or mapping of diffuse objects. No such formal distinction will be made for proposals submitted to ISAS/JAXA or to ESA.
4. All observations with total exposure times equal to or more than 300ks are open to the public immediately, this includes Long Programs in the US as well as data from Key Project observations.
5. Raster scan observations now have to have the same minimum exposure time of 10ks per pointing as other observations.
6. The XIS 2 is no longer operational. Simulations for observation time estimation should take this fact into account.
7. Using the XIS 1/8 Window option and/or the $<0.5$s frame$^{-1}$ burst option is not recommended. This option should be used at your own risk.

8. From AO-5 observations with the P-sum mode for the XIS are accepted for up to 5% of the ordinary observation time (=11902ks). In the P-sum mode a time resolution as fast as 7.8ms can be achieved. Note, however, that (1) only a 1-dimentional image can be obtained, (2) the P-sum/timing mode can only be used for XIS0 and XIS3 (not available for XIS1), (3) neither the Spaced-row Charge Injection nor a CTI correction can be applied, and hence the energy resolution is significantly worse than that in the normal clocking mode, (4) the calibration accuracy for spectral analysis is not as good as that for the normal clocking mode. Refer to section 7.5.3 for more details on the P-sum mode.

9. For feasibility studies of HXD data analyses, proposers should simulate observations with the responses and background files provided, 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).