3. Observation Policies

The prime instrument on Astro-E2 will be the XRS, a state-of-the-art, high throughput X-ray spectrometer, capable of high resolution spectroscopy over the 0.3 - 12 keV band. This instrument operates at very low temperatures (0.060 Kelvin). It is cooled using an Adiabatic Demagnetization Refrigerator (ADR) in combination with solid and liquid cryogens, which have a limited lifetime ($\sim 2.5$ years). Due to this limitation, the policy of awarding the observing time on Astro-E2 varies somewhat from that used for the recent X-ray astronomy missions such as ASCA, Chandra, or XMM-Newton. Since any observations primarily requiring instruments other than the XRS can be conducted after the cryogens are expended, priority will be given to proposals whose science objectives require the use of the XRS. Because of this, the details given in this document emphasize the XRS over the other instruments.

Over the lifetime of the XRS, the majority of all observations is reserved for Japanese, US, and ESA Guest Observers (GOs) and will be allocated via a competitive proposal review. A certain amount of the observing time is reserved for the Astro-E2 Science Working Group (SWG), which consists of the instrument, software, and operations teams, and a few external Science Advisors.

The current best estimate for the schedule of the Astro-E2 mission is given in Table 3.1. For the purpose of proposal selection, we assume 37 ksec of good on-source time per day, and 360 days of operations per year. Furthermore, observatory time (5%) and TOO time (3%) will also be reserved from this total. Therefore, the net observing time in the current AO (Phase Ib of Table 3.1) available to Japanese, US, and ESA proposers is $\sim3860$ ksec, $\sim3980$ ksec, and $\sim735$ ksec respectively. It is anticipated that an additional $\sim$ 12 calendar months of observing time with the XRS will be available in the next Astro-E2 AO (Phase Ic), and possibly more in Phase Id.

Table 3.1: The preliminary schedule for Astro-E2 and percentage of time for 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
0	$<$1	0	0 (0)	0	0
Ia	1-7	100	0 (0)	0	0
Ib	8-19	25	37.5 (6)	32.5	5
Ic	20-31	15	42.5 (7)	37.5	5
Id	32-cryogen end	0	50 (8)	37.5	12.5
II	indefinite	0	60 (10)	30	10

The nationality of the PI's institution determines which agency should receive the proposal. That is, resident researchers at US institutions must submit their proposals to NASA and those at institutions in ESA member countries must submit theirs to ESA. 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. In addition, Co-Is from any country may be part of any proposal.

In Phase Ib, 5% of the total observing time is set aside for Japan-US joint 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 5% of total time, the remainder will be divided between separate Japanese and US investigations.

3.1 Data Rights

The data rights policy for Astro-E2 is similar to previous missions. The normal exclusive period for both SWG and GO data is one year, except that all Phase Ia SWG science data will be made available at the end of Phase Ib. It is also expected that some selected targets from the SWG list will be released immediately to the community, although which targets will be released is not available as of this writing. Please check the Astro-E2 websites (see Appendix C) for updates.

3.2 Target of Opportunity (TOO) proposals

TOO proposals are allowed for Astro-E2 through the normal proposal process. However, these may only include unpredictable phenomena in a specific target (e.g. SS Cyg in outburst), not a generic target (e.g. the next Galactic supernova). The triggering criteria must be clearly defined and stated in detail in the proposal text; a brief summary should appear in the Remarks section of the target form. It will be the PI's responsibility to notify the Astro-E2 project when the criteria are met. It is anticipated that there will exist a mechanism to allow TOO proposals outside the formal proposal review process. This mechanism can be used for generic TOOs; however, the rights for this data will be determined at the Director's discretion. In addition, for gamma-ray bursts (GRBs), the SWG has allocated 200 ksec to perform coordinated observations following alerts from other monitoring satellites. Therefore, no GO TOO proposals will be accepted for additional GRBs.

3.3 Pointing constraints

The Solar panels on the Astro-E2 satellite are fixed. This places a restriction on the pointing direction with respect to the satellite-Sun line: the Sun angle constraint is normally 65 - 115 degrees. This means that at any given time of the year, only a swath of the sky 50 degrees wide is accessible for astronomical observations, and thus most celestial sources are available for observations for about 50 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 Astro-E2 proposal website (see Appendix C).

It is anticipated that long ($>$1 day) observations will be the norm for Astro-E2, based both on the Astro-E and the Astro-E2 SWG target lists. In addition, a large number of short observations is an inefficient use of the satellite because of the unusable time during slews and attitude settling. The pointing is expected to be accurate to 0.3 arcmin and can be reconstructed to better than 0.2 arcmin, except during the initial settling period of up to 10 minutes. Moreover, there is a limit on the number of slews that can be uploaded to Astro-E2. For these reasons, a minimum exposure time of 10 ksec has been set for all proposed observations. However, raster observations over a small ($< 1^\circ$) area of the sky may be allowed where the individual pointings are at least 3 ksec. For such observations, the total exposure time (which must still be at least 10 ksec) and the number of separate pointings should be entered into the RPS form. Particularly complicated operations may not be feasible; please contact either the ISAS/JAXA Astro-E2 team or the NASA Astro-E2 GOF for assistance on difficult or unusual observation plans.

There are also orbital constraints upon the orientation of the projection of the XRS array on the sky. Since the Astro-E2 XRS array is roughly square (unlike the rectangular array used for Astro-E), selecting a specific roll angle (see Fig. 2.5) is less significant. However, since support structures in the XRT-S will cross the array in a diagonal X pattern, some roll angle constraints may be useful. 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 described in §4.7. 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 XRS orientation by scheduling observations at a specific time, but for those located close to the ecliptic, the XRS will project on the sky in a nearly fixed orientation. Note that any roll constraint will make a proposal time critical. Due to their increased overhead, only a fraction of the total available time can be used for constrained observations, and proposers should justify their requirements carefully.

During a pointed observation, there will be interruptions due to the location of Astro-E2 in a low Earth orbit. Normally, a target will be occulted by the Earth for $\sim$30 minutes every satellite orbit. In addition, Astro-E2 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 other variations in the particle background, depending primarily on the cut-off rigidity^3.1. It is likely that some high background region will typically excluded from data analysis; however, the extent to which this is the case will be determined with in-orbit experiences.

3.4 Sequence of events after submission

After the Astro-E2 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; category C targets will be observed as time permits. Category A observations will be deemed to be complete when they have received at least 90% of the requested time with the XRS detector. Category B observations are considered complete after they have been observed with the XRS for 70% of the requested time. Category C observations are performed on a best-effort basis.

Even though observations are scheduled to acquire roughly the approved exposure time, and ASCA experiences suggest this will usually be achieved with Astro-E2, occasional losses of usable observation time are inevitable. Additional observations will be scheduled automatically for non-time-critical targets whose observations 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.

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 50% of the available time, category B 40%, and category C 50%.

US PIs, or US Co-Is on foreign PI projects, may propose for funding once notified that their target has been accepted. This process is described in ROSS 2004 document; further details of this process will be made available on the NASA Astro-E2 GOF website listed in Appendix C.

Each PI will be assigned a contact scientist, either at ISAS or the NASA Astro-E2 GOF, who will work with the PI to assure the maximum science return. This will include double-checking coordinates, reviewing the Filter Wheel settings, and confirming the XIS configuration. 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. Special scheduling request 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. For Phase Ib, we do not have a mechanism to approve coordinated observations with Astro-E2 and another observatory through a single proposal. It is the PI's responsibility to secure observing time with other observatories, when simultaneous observations are desirable; the Astro-E2 component of such a proposal may be approved contingent on the success of other proposals.

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. 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, all Astro-E2 software will be written as FTOOLS and distributed through the Astro-E2 team at ISAS/JAXA and the NASA/GSFC HEASARC. This includes the tools used in the processing. All calibration files will be distributed through the HEASARC caldb (Calibration Database) system. This will enable users to apply any calibration updates themselves. The Astro-E2 team at ISAS and the NASA Astro-E2 GOF will provide additional FTOOLS that may be necessary or desirable in analyzing Astro-E2 data. Use of other software packages will only be supported at a lower priority level.