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Astronomical Data Analysis Software and Systems XIII ASP Conference Series, Vol. 314, 2004 F. Ochsenbein, M. Al len, and D. Egret, eds.

MAXI Software System: Photon Event Database
Hitoshi Negoro Nihon University, 1-8-14 Kanda-Surugadai, Chiyoda, Tokyo 101-8308 Japan M. Kohama, T.Mihara RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan N. Kuramata, H. Tomida, S. Ueno, H. Katayama, M. Matsuoka JAXA, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505, Japan Y. Serino, N. Kawai Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan T. Arakuni, A. Yoshida Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara, Kanagawa 229-8558, Japan Abstract. MAXI is an X-ray all-sky monitor loaded onto the Japanese Experiment Module of the International Space Station (ISS) from 2008. MAXI monitors more than 103 X-ray sources, and provides quasi-realtime data of, for instance, AGN variability and X-ray Novae through the internet. Each X-ray event is stored into the MAXI databases on the ground as a single data record. As a result, the databases contain more than 100 Giga records with 0.2 - 1 TB in 2 years mission life. We have just built this first huge 'photon event' database for low-speed Mil-1553b interface data.

1.

MAXI and Database

MAXI is an X-ray all-sky monitor which will be loaded onto the Japanese Experiment Module (JEM, "Kibo") of the International Space Station from 2008 (Matsuoka et al. 1997). MAXI scans the whole sky in every 90 minutes with the sensitivity of as high as 7 mCrab (5 sigma level), reaching a detection limit of 1 mCrab in one-week. Thus, MAXI will continuously monitor X-ray time variability of a number of AGNs over a period of two years (Kawai et al. 2003). MAXI has two kinds of X-ray detectors: Gas Slit Camera (GSC, see Mihara et al. 2002 in detail) and Solid-state Slit Camera (SSC, also see Miyata et al. 2002). The GSC consists of twelve identical position-sensitive proportional 452 c Copyright 2004 Astronomical Society of the Pacific. All rights reserved.


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counters with the total area of 5,000 cm2 , and covers an energy range of 2-30 keV. The source direction is determined with the long rectangular field-of-view (1.5в80 degrees) and a charge division method in the detectors. A set of three cameras covers 1.5в160 degrees in an arc. While, the SSC consists of 32 X-ray CCD chips (1 inch square). It covers a soft energy (0.5-10 keV) band with a high energy resolution in spite of a relatively small total effective area ( 200 cm2 ), and complementarily works with the GSC. Relatively large spatial resolution ( 1.5 deg) of the detectors prevents us from instantaneously determining a source direction for each X-ray. Furthermore, directions of the detectors change every moment due to the ISS orbital revolution. These and a large amount of data prevent us from building a normal database for pointing observations or for monitoring observations (for instance, the database for RXTE ASM1 ). Instead, we have tried to build the first 'photonevent' astronomical database for this mission. This will make it easy to produce any kind of light curves, images and energy spectra for given periods and/or directions, suitable for highly variable sources. It will take much time (order of 1 TB/100 MB/s 104 s) to do this for each source from raw telemetry data without such a database. Here, we briefly introduce the MAXI software system and the present status. 2. Data and Download

X-ray event data, house-keeping (HK) data and health and status (H&S) data are processed in parallel by the on-board data processor (DP) with 4 MIPS R3081 CPUs and VME bus (developed by NEC TOSHIBA Space Systems, Ltd, NTSpace). Using two interfaces on ISS (Table 1), the data are downloaded to the NASA and JAXA ground stations through the two relay satellites, TDRS and DRTS, respectively (Fig. 1). All the data are once stored to a database in the Operations Control System (OCS) at JAXA in Tsukuba and transferred to our 1553b and Ethernet databases (individual databases for a security reason). The low-speed Mil-1553b interface is mostly available and is believed to be the most robust though the band-path is limited. Our system is designed so we can achieve a minimum scientific goal even if the medium-speed Ethernet interface is unavailable. For instance, GSC and SSC 64-bit data are degraded to 16-bit data with the DP, and downloaded through the 1553b interface. Table 1. Summary of two ISS interfaces for MAXI. Interface low-speed Mil-1553b medium-speed Ethernet Trasfer-Rate 20-50 kbps 200 kbps Availability 17 hr/day 4­5 hr/day Data H&S and summary full data set

1

http://xte.mit.edu


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Negoro et al.
Data Flow Work Flow

1553B data @ MAXI room at JAXA, Tsukuba, Ibaraki
U-BIS

TDRS @NASA 2002~2004
1553B DB System

H&S Check QL (GSE) System

OCS@JAXA

Proto-type of Ether DB Sys Simulator

2003~2005
Detector Status Nova Search

MAXI/DP

ISS

1998~2005

2004~
Ethernet DB System Data Analysis System

DRTS @NASDA ~2006~
Data Archive System

~2005~

2008~

World
Figure 1.

Ethernet data @ MAXI room at RIKEN, Wako, Saitama

MAXI data and work flows and software road-map.

3. 3.1.

Database System for 1553b Data sub-Tera order records

We have just built the 1553b database. Currently, the database contains 1807 items in 81 tables. Most items are accumulated every second, and 100­200 X-ray event/sec are expected in orbit. As a result, the total number of the records in 2 years mission life will be 2000 в 86, 400 (s/d) в365 (d/y) в2 (y) 1.2 в 1011, and the total size of the database roughly 1.2 в 1011 в 2 - 8 byte 0.2 - 1 TB. The database itself is developed by Systems Engineering Consultants Co., Ltd. (SEC)2 , and made with Java 1.4.x using ORBD and JDBC in order to make the system free from hard and softwares as best as possible. 3.2. Flexible and Scalable

The system should be flexible and scalable, because data items and hardwares have not yet been fixed. (We do not know what kinds of OSs survive in future, and how much hardwares will progress.) We describe all the data information (item name, C type, DB information, address in telemetry data, and so on) in a spreadsheet file. All the data-dependent parts in the system are automatically produced from this file even if some modifications are necessary (Fig. 2).

2

http://www.sec.co.jp


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OCS DB 1553B telemetry data spreadsheet "db_table_xx.xls"

Documents and Manuals
TeX

information about data location and boundaries to be checked
SEC DB system data resolver program

definitions of structures definitions of tables and those members information to pack table data into structures User QL system
User Window User C program structure 1 structure 2 structure 3 simple socket interface reformat Java (JDBC)

table 1 table 2 table 3

RDB

Figure 2. 3.3.

Spreadsheet and its productions

Current Status

We are now testing the database at RIKEN in various hardware environments (different CPUs and hard disks) using PostgreSQL 7.3.x. We are also planning to test Sybase ASE 12.5 and Oracle 9i to find the best (cost) performance environment. The DB system is so large that data access time will be a serious problem. This is our main concern at the moment in this test. How to divide data into (small) tables will be a key to solve the problem. Detailed results will be reported elsewhere. References Kawai, N., Negoro, H., Yoshida, A., Mihara, T. (Eds.), 2003, in MAXI Workshop on AGN Variability, (Seiyo Press: Tokyo) Matsuoka, M. et al., 1997, SPIE, 3114, 414 Mihara, T. et al., 2002, SPIE, 4497, 173 Miyata, E. et al., 2002, SPIE, 4497, 11