Monitor of All-sky X-ray Image (MAXI) mission on ISS/JEM

Tatehiro Mihara$^1$, Nobuyuki Kawai$^1$, Atsumasa Yoshida$^1$, 
Hitoshi Negoro$^1$, Ikuya Sakurai$^1$,
Masaru Matsuoka$^2$, Shiro Ueno$^2$, Mutsumi Sugizaki$^2$, 
Yuji Shirasaki$^2$, Weiming Yuan$^2$,
Hiroshi Tomida$^2$,  Ken'ichi Torii$^2$, Masaaki Sakano$^2$,
Hiroshi Tsunemi$^3$, Emi Miyata$^3$,
Isao Tanaka$^4$

$^1$RIKEN, Wako, Saitama, Japan \newline
$^2$NASDA, Tsukuba, Ibaraki, Japan \newline
$^3$Osaka University, Toyonaka, Osaka, Japan \newline
$^4$Graduate University for Advanced Studies, Japan


MAXI is an X-ray all-sky monitor which will be mounted on the Japanese
Experiment Module of the International Space Station.  MAXI scans the
whole sky in every 90 minutes.  The sensitivity will be as high as 7
mCrab (5 sigma level) in one scan and 1 mCrab in one-week
accumulation.  Thus MAXI can monitor the X-ray intensities of the
bright AGNs over more than two years.  MAXI consists of two kinds of
X-ray detectors: Gas Slit Camera (GSC) and Solid-state Slit Camera
(SSC).

The GSC consists of twelve position-sensitive proportional counters
with Xe+CO$_2$ gas and carbon fiber anodes of 10$\mu$m diameter. The
window size is 272$\times$190 mm (about A4 paper size), which makes
the total area of $\sim$ 5000 cm$^2$.  The position is obtained by the
charge division method.  It is used to identify the source in the long
rectangular field-of-view (1.5$\times$80 degrees).  Three cameras will
be set to cover the 1.5$\times$160 degrees arc.

The SSC consists of 32 X-ray CCD chips (1 inch square) which are
developed by Hamamatsu Photonics.  The total area is $\sim$ 200
cm$^2$.  Each CCD chip is cooled by one-stage peltier device. The
operating temperature is estimated to be $-60 \sim -50$ $^\circ$C at
the end of mission life.  Therefore, the CCD chips need to have not
only high detection efficiency and low readout noise, but also the low
dark current.