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2. Observations Types

In this chapter, we provide a brief description of various types of Suzaku observations, because different types of observations are treated differently in data distribution and archiving.

Figure 2.1 shows a flowchart illustrating various processes in the Suzaku observation program from GOs' proposal submission to the data reception. Important issues for individual processes outlined in this chapter are explained in more details in later chapters.

Figure 2.1: Overview of the Suzaku mission operation and observation program.

2.1 Observations Types

2.1.1 In-Orbit Checkout

The period between the launch on July 10, 2005 and the end of August, 2005 is considered the in-orbit checkout (IOC) phase. The first part of this phase was devoted to engineering activities, and no celestial X-ray sources were observed. After the XIS first light on August 12 and the HXD first light on August 15, observations of celestial X-ray sources were carried out. Telemetry data after August 12 are processed normally, although care must be taken as instrument parameters are not necessarily the same as for later observations.

2.1.2 Observatory Time

Throughout the Suzaku mission life, approximately $\sim$12 % of the time will be reserved as the Observatory Time. It will be used, for example, for instrumental calibration, maintenance of the satellite, or to compensate for unexpected observational/operational failure such as cancellation of the ground contacts due to bad weather. Target of opportunity (TOO) observations (section 2.1.6) may be also carried out using the Observatory Time.

2.1.3 Science Working Group Time

Suzaku Science Working Group (SWG) is the collective name given to the instrument teams, mission operations team, software and processing team, as well as Science Advisers who were selected to provide guidance to the Suzaku team.

During the period between September 2005 and March 2006, the scientific (non-Observatory Time) observations were generally selected by, and conducted by the SWG. This period is often referred to as the SWG phase of the mission. No new SWG observations were included into the observing program after April 2007, although a few SWG observations were carried out later, usually because of a problem with the original observations. All SWG observations were completed by October 2006.

2.1.4 GO Observations

Suzaku entered the guest observer (GO) phase of the mission in April 2006. During this period, all non-Observatory Time observations are selected from the world-wide astronomy community, with the exception of the delayed SWG observations (see above). Some GO observations were carried out in February and March 2006, before the nominal start of the GO period.

Targets are selected through a competitive process from observing proposals submitted by guest observers (GOs). Proposals by principal investigators (PIs) affiliated with a US institution are submitted to, and selected by, NASA, through the annual NASA Research Announcement (NRA) process.

PIs affiliated with an institution in an ESA member country submit their proposals through ESA, who conduct their own proposal review. Proposals submitted to ISAS/JAXA (principally by Japanese PIs, although PIs from non-US, non-ESA country may also apply through ISAS/JAXA) are judged by ISAS. The ESA list is folded into the Japanese list.

The final accepted target list is determined at the Japan-US merging meeting based on the Japanese (including ESA) and US target lists. In case there are identical targets on the Japanese and US target lists, the same target may be assigned to a Japanese PI and a US PI. Such targets are referred to as ``merged.''

The GOF serves as the principal point of contact for US PIs, including co-PIs of merged targets. This includes observation planning, notification of availability of processed data, and support in analyzing the processed data (chapter 8).

2.1.5 Calibration Observations

Suzaku team will regularly carry out calibration observations to monitor the performance of the instruments. Calibration observations are carried out using the Observatory Time.

2.1.6 Target of Opportunity Observations

Targets of Opportunity (TOOs) are observations of objects or states of objects that cannot be predicted. X-ray novae, supernovae, strong flares of known targets, and after-glows of Gamma-ray bursts (GRBs) are examples of TOO targets.

TOO observations may enter the Suzaku observing program in one of two possible ways. Pre-approved TOOs are part of the GO observations, and are limited to unpredictable phenomena on specific, known objects. In addition, genuinely unpredictable objects or events can be observed as part of the Observatory Time.

2.1.7 HXD WAM Observations

The anti-coincidence detectors of the HXD can be used to detect GRBs and to monitor the flux levels of bright hard X-ray/$\gamma$-ray sources. This aspect of the HXD is known as the Wide-band All-sky Monitor (WAM). Even during the GO phase, the WAM data do not belong exclusively to the PI.

2.2 Proprietary Period

The SWG data are proprietary to the SWG until May 27, 2007, or 1 year after the date of observation, whichever is later. In general, GO observation has a proprietary period of 1 year after the delivery of the processed data. The project may extend the proprietary period of GO data in cases where a lack of analysis software or calibration data seriously impacted the usefulness of the data. In such cases, the proprietary period will extend 1 year after the availability of the software/calibration data, as judged by the project. Calibration observations and TOO observations taken using the Observatory Time during the GO phase have no proprietary time.

Proprietary data are available for download in encrypted form. The decryption keys are supplied to the PIs, who may share them with their co-investigators. After the proprietary period is over, the decrypted data are placed in the Suzaku archives (section 2.4.4; chapter 9), and open to all interested researchers.

2.3 Satellite and Instrument Monitoring

Duty scientists will monitor the health and safety of the satellite and the instruments, both at the downlink station at the Uchinoura Space Center (USC) and at ISAS. They may not carry out scientific analysis of the data. Any scientific insights incidentally gained by the duty scientists are considered confidential.

Certain aspects of the data are considered non-proprietary. In addition to the HXD/WAM data, they include any data during which the instruments are pointed at the Earth, and XIS data from the area of the CCD chips dominated by the on-board calibration source. Such data can be placed in the trend archive in unencrypted form, even during the proprietary period for that observation.

In addition, the instrumental teams may access proprietary data for the purpose of monitoring the performance of the instruments. They must refrain from performing any scientific analysis of the data, and keep any knowledge incidentally gained while performing their duties confidential.

2.4 Data Flow

2.4.1 Data Retrieval and Raw Data Archives

The data are retrieved from the satellite only at USC. Suzaku has the data recorder with the 6 Gbits data capacity and can downlink the data to USC by up to $\sim$10 Gbits daily in 5 contact passes. Raw data are sent from USC to ISAS through a dedicated network, and saved in the raw database named SIRIUS. The SIRIUS database at ISAS stores the raw telemetry data of all the current and past ISAS missions.

2.4.2 Data Processing at ISAS and GSFC

The Suzaku data processing means conversion from the raw telemetry data to the high-level calibrated data deliverable to the Suzaku Observers. Details of the data processing are explained at section 6.1, and only an outline is given here (figure 2.1).

At ISAS, telemetry files in the SIRIUS database are wrapped into portable Raw Packet Telemetry (RPT) FITS files, with a minimum set of FITS keywords. Routinely, ISAS will process RPT files to produce First FITS Files, which conform to high level FITS standards.

Attitude of the satellite and the clock correction is calculated at ISAS, and the satellite orbit is determined2.1. The First FITS Files, attitude files, orbit files and timing correction files constitute a complete data package for each observational sequence. These packages are archived at ISAS, and the identical copies are delivered to GSFC regularly. The RPT files are also delivered to GSFC for archival and back-up purposes, so that the First FITS Files may be produced at GSFC if necessary.

The same Pipe-line Processing runs on the First FITS Files at ISAS and GSFC, to apply the calibration information and to produce the high-level processing products (section 6.6).

2.4.3 Data Delivery to Suzaku Observers

The processing products are delivered to the Guest Observer or the SWG members, as appropriate. US Suzaku Observers will receive data from GSFC, and Japanese Observers will receive from ISAS. The proprietary data are placed in on the Suzaku archives with a secure data protection method such as the PGP encryption.

Suzaku Observers will be able to conduct scientific analysis immediately from the processing products. The analysis software and user support are provided by the Suzaku GOF (see chapter 3, 4 and 8).

2.4.4 Suzaku Archives

All the Suzaku data will be delivered to and archived at the HEASARC at NASA/GSFC and to the PLAIN Center at ISAS/JAXA. After the proprietary period is over, the data are made public (i.e., decrypted version will be made available), so that archive users are able to obtain exactly the same datasets as the original Guest Observers have received. From time to time, contents of the archives ma be updated, after being reprocessed with updated software and calibration files. Details of the Suzaku archives are explained in chapter 9.

next up previous contents index
Next: 3. Software Principles Up: Suzaku Project Data Management Previous: 1. Introduction   Contents   Index
Michael Arida 2007-09-29