PASJ: Publ. Astron. Soc. Japan 62, 1371–1379, 2010 December 25
c 2010. Astronomical Society of Japan.
In-Orbit Performance of the MAXI/SSC onboard the ISS
Hiroshi T SUNEMI,1 Hiroshi T OMIDA,2 Haruyoshi K ATAYAMA,3 Masashi K IMURA,1
Arata DAIKYUJI,4 Kazuhisa M IYAGUCHI,5 Kentaro M AEDA,5 and the MAXI team1
1 Department of Earth and Space Science, Graduate School of Science, Osaka University,

1-1 Machikaneyama, Toyonaka, Osaka 560-0043
tsunemi@ess.sci.osaka-u.ac.jp
2 ISS Science Project Office, ISAS, JAXA, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505
3 Earth Observation Research Center, JAXA, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505
4 Department of Applied Physics, Faculty of Engineering, University of Miyazaki,
1-1 Gakuen Kibana-dai Nishi, Miyazaki, Miyazaki 889-2192
5 Solid State Division, Hamamatsu Photonics K.K., 1126-1 Ichino, Hamamatsu 435-8558(Received 2010 July 9; accepted 2010 August 5)

Abstract
We report here the in-orbit performance of the CCD camera (MAXI/SSC) onboard the International Space
Station (ISS). It was commissioned in 2009 August. This is the first all-sky survey mission employing X-ray CCDs.
It consists of 32 CCDs, each of which is 1 inch square. It is a slit camera with a field of view of 1:ı 5  90ı , andscans the sky as the rotation of the ISS. The CCD on the SSC is cooled down to the working temperature around60ı C by the combination of a peltier cooler, a loop heat pipe and a radiator. The standard observation mode of the
CCD is in a parallel sum mode (64-binning). The CCD functions properly, although it suffers an edge glow when
the Sun is near the field of view (FOV), which reduces the observation efficiency of the SSC down to about 30%.
The performance of the CCD is continuously monitored both by the Mn-K X-rays and by the Cu-K X-rays. There
are many sources detected, not only point sources, but extended sources. Due to the lack of an effective observation
time, we need more observation time to obtain an extended emission analysis extraction process.
Key words: instrumentation: detectors — space vehicles: instruments — X-ray CCDs

1. Introduction
The ASCA satellite (Tanaka et al. 1994) was the firstsuccessful mission that carried X-ray CCDs in the photoncounting mode (Burke et al. 1991). Since then, the X-ray CCDs
in the photon-counting mode have become the standard X-ray
detectors for X-ray astronomy missions. Chandra (Weisskopf
et al. 2002), launched in 1999, carries the ACIS consisting of
10 CCD chips, each of which is one inch square in imaging
area. XMM-Newton launched in 1999 carries the EPIC, which
consists of two CCD cameras: one is a MOS camera (Turner
et al. 2001) and the other is a pn camera (Strüder et al. 2001).
The MOS camera consists of 7 CCD chips, each of which is
4 cm square. The pn camera has one CCD chip that is 6 cm
square. The Swift satellite launched in 2004 (Gehrels et al.
2004) carries one CCD chip, which is identical to those of the
MOS camera. The Suzaku satellite launched in 2005 carries
the XIS (Koyama et al. 2007) consisting of 4 CCD chips, which
are improved CCDs of the ACIS.
The MAXI (Monitor of All-sky X-ray Image: Matsuoka
et al. 2009) was planned in 1998 to be launched in 2003. There
are two cameras: the Gas Slit Camera (GSC: T. Mihara et al. in
preparation) and the Solid-state Slit Camera (SSC). The SSC
was proposed to be an array of X-ray CCD onboard the MAXI.
This is a slit camera: a kind of a pin hole camera. It carries 32
CCD chips, each of which is one inch square. Due to an unexpected problem of the ACIS in orbit (Weisskopf et al. 2002),
we introduced a continuous function of the charge injection

so that we could recover any radiation damage on the CCD.
This technique (Prigozhin et al. 2008) is added to the XIS in
orbit and improves the performance of the CCD (Uchiyama
et al. 2009). Then, the MAXI was successfully launched in2009 July by a space shuttle, Endeavor, and was installed to
the Japanese Experiment Module — Exposed Facility (JEMEF) on the International Space Station (ISS).
We report here on the basic structure, calibration and in-orbit
performance of the SSC.
2. SSC Structure and Its Thermal Performance in Orbit
The SSC is installed on the GSC, which is described in detail(Matsuoka et al. 2009). There are two cameras: SSC-H and
SSC-Z. Each has 16 CCD chips, and is identical to each otherwith the exception that the SSC-H is watching +20ı above
the horizontal direction of the ISS and the SSC-Z is watching
the zenith direction of the ISS. We aligned 16 CCD chips ina 2  8 array.
2.1. CCD for the MAXI/SSC
We developed the CCD for X-ray detection (Tsunemi et al.
2007) under collaboration with Hamamatsu Photonics K.K.,
table 1 shows the structural parameters of the CCD (Katayama
et al. 2005). Since there is no storage area, it works in a fullframe mode. The X-ray entrance surface has an Al coat toprevent visible light from entering. The Al coat on the CCD
enables it to eliminate an optical blocking filter in front of

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Table 1. MAXI-CCD parameters.

IA # of pixels
IA pixelType# of nodes
Wafer typeCoat1024  1024
24 m  24 m
Front-illuminated1p-typeAl (2000 Å)the CCD. This also makes it possible to eliminate a vacuumtight body. The CCD has a thick depletion layer by using
a high-resistivity wafer. Based on the design parameters andthe ground calibration (Tomida et al. 2010), we calculated
the quantum efficiency (QE), which is shown in the literature(Matsuoka et al. 2009). In the next section, we improve theaccuracy of the QE calibrated in orbit by using the Crab nebula.
2.2. Thermal Performance in Orbit
The use of CCDs for X-ray detection requires a low working
temperature. The cooling system of the MAXI/SSC consistsof two parts: one is a peltier device, and the other is a radiatorwith a loop heat pipe (LHP).
The hot side of the peltier is thermally connected to the bodyof the SSC. The body of the SSC is cooled down to around20ı C, and depends on thermal condition of the radiator. The
radiator consists of two panels: an upper panel (Radiator Z :0.527 m2 ) and a forward panel (Radiator H : 0.357 m2 ). They
are designed such that we can obtain the maximum area within
the allocated volume of the MAXI. Since these two panels are
not in the same plane, the LHP is designed to cool down the
body of the SSC as much as we can. After launch, the LHP
started properly, and is working as we expected. The radiatortemperature depends on the ISS location and its orientation,
but there has been no decrease in the cooling power as of thewriting phase of this paper.
There are two means of temperature control. One is to keep
the CCD temperature constant, while the other is to keep the
peltier current constant. Since we selected the latter mean in
the present operation of the SSC, the temperature of the CCDchanged as the radiator temperature changed. Figure 1 shows
the temperature history of the CCD after the launch, where
each point represents the one-day averaged temperature. Twopanels of the radiator show different thermal behavior, whose
temperature is between 25ı C and 55ı C. The LHP cools
down the SSC body to around 20ı C. The peltier device cools
down the CCD to around 60ı C. Since the peltier is runningin constant-current mode, the temperature difference is also
constant at around 45ı C, depending on the individual peltier
device. The detailed spectral analysis takes into account theworking condition of the SSC.
3. Onboard Data Process
The data-handling scheme of the MAXI/SSC is similar tothat of previous satellites. A detailed explanation is given in
the literature (Tomida et al. 2010). There is one video chain
for each camera (16 CCDs). MAXI is designed to observe
not in a pointing mode, but in a scanning mode. We have two

Fig. 1. Temperature histories of the CCD, the SSC body and twopanels of the radiator are shown since the launch of the MAXI/SSC.
We show temperatures for 4 CCDs out of 32.

data-taking modes: one is the full-frame mode, and the other isthe parallel-sum mode. The full-frame mode is used to obtainan image of 1024  1024 pixels for each CCD. The full-frame
mode is only used to check the performance of the CCD, since
the time resolution is very bad due to the telemetry capacity.
The parallel-sum mode is used to add up many pixel signals
to speed up the read-out time. In the standard observation of
the MAXI/SSC, we add 64 rows as an on-chip sum while otherbinning is possible by command. Because we employ a charge
injection at every 64 rows, we skip the charge injected row
and accumulate 63 rows for binning. In this way, we obtain16  1024 pixels for each CCD. Since we sequentially read
16 CCD chips, the read-out time is 5.865 s that depends on
the number of rows of the on-chip sum. We should note thateach CCD will have an integration time of 5.498 s, followed
by a read-out time of 0.367 s, since one read-out video chain
reads 16 CCDs one by one. This makes it possible to partly
determine the incident position of the X-ray photon within the
CCD. In this way, we can measure the CTI of the CCD, evenin the parallel-sum mode.
We employ an event recognition method similar to the
ASCA grade. In the parallel-sum mode, the charge spread of
the signal is effectively valid only for G0 (single event), G1(left split event), G2 (right split event) and G3 (three-pixel
event). Since we do not see the charge spread in the verticaldirection, the background rejection efficiency is worse thanthat of the normal mode in other satellites. We expect that the
X-ray events form G0, G1, or G2, while the charged particle
event forms G3.
Figure 2 shows typical frame images obtained in orbit. The
night-time image shows X-ray events and particle events aswell as some fixed patterns due to CCD operation. The daytime image shows overflow in the edge area of the CCD.
During the day time, direct Sun light enters through the slit,
and is scattered inside the collimator, even if the Sun does notilluminate on the CCD. In the central part of the CCD, the Sun
light is well blocked by the Al coat. Because the edge of the
Si wafer of the CCD is left un-coated, Sun light penetrates into

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Fig. 2. Frame images obtained at night (left), and during the day (right). Each frame consists of 1024  1024 pixels, which is used for diagnostics. In
the normal observation mode, the parallel sum mode (64 binning) is employed.

the CCD. Since the edge glow appears only in the day timeobservation, we think that bright IR light enters the CCD
through the edge of the CCD.
By looking at the night-time image, we can handle theparallel sum-mode data as other satellites do. The day-time
image indicates that pixels on the edge of the CCD show saturation in the electronics. Therefore, only a central part ofthe image can be analyzed. In the parallel-sum mode in 64binning, the effective area is reduced by 70%. Furthermore,
the background is quite different from that of the night-time
image. We are still studying how to use the day-time image.
4. Calibration
4.1. Performance of the CCD in Orbit
Radio-active sources of 55 Fe are installed at the edge ofthe cameras inside the MAXI/SSC. We also obtain continuous
monitoring of Cu-K lines produced at the collimator by theincident particles. Figure 3 shows the spectra for 32 CCDs,
each of which shows Cu-K lines. By using these lines, we
can continuously monitor the performance of the CCD. The
intensity of Cu-K lines is about 0.08 counts s1 per CCD, andthat of Mn-K lines was about 0.05 counts s1 per CCD at thetime of launch.
Figure 4 shows the history of the Cu-K peak position and its
energy resolution (full width at half maximum: FWHM). Eachpoint represents the data for one-day accumulation time. The
FWHM of Mn-K˛ is 147 eV and that of Cu-K˛ is 170 eV at thetime of launch. Mn-K is irradiated onto the far side from theread-out node of 4 CCDs while Cu-K is irradiated uniformly
over all of CCDs.
The ISS is in a circular orbit of altitude around 350 km
and inclination of 51:ı 6. It passes through the South Atlantic
Anomaly (SAA) 9–10 times a day. Furthermore, it passes

through a high-background region at high latitude. The background is monitored by the RBM onboard the GSC (Sugizaki
et al. 2010). It shows that 15% of the time is high background due to SAA passage. Furthermore, it shows that thepassage through high latitude also shows high background. The
background spectra for these two passages may be different,
whereas they are so high that the GSC turns off duringobservations.
The CCD employed has two characteristics for radiationhardness. One is a notch structure that confines the chargetransfer channel to a very narrow width. This improves theradiation-hardness by a factor of three (Tsunemi et al. 2004).
The other is a charge-injection (CI) gate through which we cancontinuously inject some amount of charge at every 64 rows in
the 64 binning mode (Miyata et al. 2002). The CI method canpartly compensate for any degradation of the charge transfer
inefficiency (CTI) of the CCD (Tomida et al. 1997). We canconfirm the validity of the CI by stopping operation of the CI.
As of the writing phase of this paper (8 months after launch),
we found that the decay of the Cu-K line of about 1% yr1
without CI, while it improves to be less than 0.2% yr1 with CI.
The decay of the FWHM at 6 keV is estimated to be 60 eV yr1 .
This value is more than we expected before launch (Miyata
et al. 2002).
The Suzaku XIS employs CI in orbit (Prigozhin et al. 2008).
CI of the XIS (FI) improved the decay of the 6 keV line from
1.6% yr1 to 0.4% yr1 . It also improves the decay of the
FWHM at 6 keV from 60 eV yr1 to 20 eV yr1 . Therefore,
the performance of the CI on the XIS is better than that of
the SSC. There are two differences between the XIS and theSSC. One is the working temperature. The XIS is working
at 90ı C, while the SSC is working at 60ı C. The otheris the background condition. The high background passage
time is 55% for the MAXI/SSC, while it is 10% for Suzaku.

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Fig. 3. Spectra for Cu-K lines for 32 CCDs. The effective energy ranges of some CCDs are limited below 9 keV due to the electronics.

4.2. Background of the SSC in Orbit

Fig. 4. History of the energy resolution (FWHM) at the Cu-K line
shown since launch of MAXI/SSC.

Although the effect of the background passage depends on the
spectrum and its intensity, the difference between Suzaku and
MAXI/SSC is due to the difference in the orbit, mainly in the
inclination angle.

The background condition is carefully monitored by the
RBM and the GSC on MAXI, since the inclination of the ISS
orbit is 51:ı 6, resulting in passing at higher-latitude regions
than other X-ray missions. We switch off the bias level to
the CCD during passage of the SAA (Miyata et al. 2003).
However, we switch on during the passage of high-latitude
regions where the background is too high to obtain good data.
Figure 5 shows the frame image obtained near the highbackground region [W108:ı6, N49:ı 4, cut-off-rigidity (COR)= 1.0 GeV c1 ] at the same exposure time at 2010 April 21
8:34. We can clearly see many particle events on both the
SSC-H and the SSC-Z. The SSC-H image shows many circularextended events that are generated by particles entering into
the CCD along the normal to the CCD surface. The SSC-Z
image shows events of long trajectories that run within thedepletion layer. The number of particle events on the SSC-H
image is about 10-times more than that of the SSC-Z. This
indicates that the cross-section against the particle flux is muchbigger in SSC-H than that in SSC-Z. Taking into account thefact that the direction of the geomagnetic field is 74ı downward from the horizon, the normal of the SSC-Z is almost
parallel to the geomagnetic field line, while that of the SSC-H

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Fig. 5. Frame images are shown at a high-background region. The left image was obtained from the SSC-H and the right from the SSC-Z.

Fig. 6. Background spectrum for G0 and G1+ G2.

is almost perpendicular to it. Since the high backgroundcomes from trapped charged particles by the geomagnetic field,
their moving direction is almost in the horizontal direction.
Therefore, they leave events of long trajectories with less fluxin the SSC-Z, while they leave circular extended events withmore flux in the SSC-H.
We accumulated data during times when the backgroundlevel was low. All of the events were sorted according to
the grade; G0, G1, G2, and G3. G3 is thought to be generated from particle events. Figure 6 shows the spectra for G0
and G1 + G2.
The G0 spectrum shows two components dividing at 0.6 keV.
The G1 + G2 spectrum has three components dividing at
1.3 keV and 0.7 keV. We found that the G1 spectrum below
0.6 keV is produced by particles having long trajectory on
the CCD. The very end of the trajectories sometimes leaves
G0 events. If they leave adjacent two pixels, they will form

G1 or G2 events that extend the spectrum of G1 and G2
up to 1.3 keV. If they leave more than three pixels, they
will be treated as particle background. The peaks around
0.7 keV on the G1 + G2 spectra come from the event threshold(0.4 keV). In this way, we find that the parallel-sum modeon the MAXI/SSC generates high background at low energy,
depending on the grade.
Figure 7 shows the background spectra of G0 + G1 + G2.
We clearly see the anti-correlation between the intensity andthe COR. Furthermore, the spectral shape is almost constant.
Therefore, we have to sort the data by the COR. Since weobserve the sky in a scanning mode, it is relatively easy to estimate the background for point sources. However, it is difficult
to estimate the background for extended structures. A precise
analysis for extended sources requires us to study the background behavior as a function of the COR.
Hiraga et al. (2001) measured the charge spread in the CCD
as a function of the mean absorption length in Si. Then, we cancalculate the branching ratio for X-ray events. For example,
the Al-K X-rays generate 92% for G0 and others for G1 and G2
that is confirmed by the ground calibration. From figure 6, we
can see that the fraction of G1 and G2 increases as a functionof the energy, particularly above 5 keV. This indicates that the
charge spread increases as a function of the energy. Taking
into account the background condition, we used only G0 events
for the energy range below the Si-K edge and G0 + G1 + G2
events for the energy range above it.
4.3. Calibration of the Quantum Efficiency
We accumulated data for the Crab nebula, shown in figure 8.
When we fit the data by a power-law with the interstellar
absorption feature, NH , and the quantum efficiency (QE) of the
pre-launch data (Matsuoka et al. 2009), we obtained a powerlaw index  of 2.2 and an NH of 6  1021 cm2 . These aredifferent values from those obtained in the previous literature(Kirsch et al. 2005). With taking into account the energy range

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Fig. 7. Background spectrum of G0 + G1 + G2 for various levels of the COR.

Fig. 8. X-ray spectrum of the Crab nebula obtained by the SSC-H and the SSC-Z. The solid lines show the best-fit model (power law + NH ).

of the SSC, we find that the parameters for the Crab nebula as is 2.1 of NH of 3.8  1021 cm2 . This indicates that we needfurther calibration.
The CCD employed has a Si depletion layer above which
there are SiO2 insulator, Si gate and Al coat. We leave thoseparameters free so that we can reproduce the Crab nebula spectrum mentioned above. The best-fit parameters are given intable 2 as well as the design values. The difference may
come from possible contamination, which will be checked infuture calibrations.
The spectrum obtained is the integration of all data. The
MAXI/SSC detected the Crab nebula with various acquisition
angles (0ı –40ı ). The best-fit parameters are converted to theTable 2. Spectrum fit for the Crab nebula.

Layer

Design value

Derived value

Depletion layer [Si]Gate [Si]Insulator [SiO2 ]Optical block [Al]70 m0.3 m0.8 m0.2 m75 ˙ 3 m
0.39˙ 0.02 m
0.79˙ 0.04 m
0.21˙ 0.01 mobservation of the acquisition angle at 0ı . In a real data analysis, we need to modify the QE, while taking into accountthe acquisition angle. Figure 9 shows the revised QE for
the MAXI/SSC.

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5. Scan Observation
MAXI/SSC observes the sky with an FOV of 1:ı 5  90ı ineach camera. The angular response along the scanning direction is set by the collimator, resulting in a trianglar shape. The
perpendicular direction is limited by the slit. Since the position
resolution is limited by the CCD pixel size, it shows a box-car
shape. The FOV moves with the ISS rotation around Earth.
Therefore, the on-source time is about 45 s. Figure 10 shows
the distribution of photons on the sky when the Sco X-1 andthe Crab nebula pass the FOV. The figure for the Sco X-1
comes from a single scan. The source is generally detected by
two CCD chips out of 16 chips. Therefore, the data are taken
two times in one read-out cycle (5.865 s). We see several line

1377

segments that are separated by about 2.9 s.
The figure for the Crab nebula comes from the data of
one-day integration, where we also see a recurrent novaof A 0535+26 (Sugizaki et al. 2009). We see that the
Crab nebula gives us 80 counts/scan. The SSC can detects
1300 photons/day from the Crab nebula if it is in the acquisition angle of 0ı . The background level of the SSC is about
150 photons/day/PSF. We find that the Crab nebula is detected
at the 100  confidence level in one-day integration data.
Therefore, the detection limit of the SSC is about 50 mCrab(5 ) for a one-day observation. It becomes about 200 mCrab
for single scans.
The CCD chip of the SSC can detect about
200 photons cm2 (read-out time)1 if we set the pile-up
events to be less than 10%. In the normal operation mode,
this value corresponds to 80 photons cm2 s1 , which is 25
Crab nebula intensity. Therefore, we can expect that a source
like the Sco X-1 is almost pile-up free, even at the centerof the FOV.
6. All Sky Map

Fig. 9. QE of the SSC calibrated by the Crab nebula spectrum.
We employ G0 for E  1.8 keV and G0 + G1 + G2 for E  1.8 keV.

The SSC observes the sky all of the time. Only at the passageof the SAA and at the time when the Sun is very close to theFOV, do we switch off the bias voltage applied to the CCD. The
data are subject to the edge glow problem during a day-timeobservation. Therefore, the effective observation efficiency is
expected to be about 30%. In the first 6 months after launch,
we had occasional problems in one of the two data-transfer
systems. When we had a problem, we had to turn the MAXI
off to recover. This reduced the data-taking efficiency down
to 20% or less. The problem was finally fixed by adding an
extra router by an astronaut who was transported with the space
shuttle in 2010 February.

Fig. 10. Singe scan image of the Sco X-1 (left) and one-day integration data of the Crab nebula (right). Since the read-out time is 5.865 s, the data along
the scan direction is quantized in the left figure.

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Fig. 11. All sky image obtained by the SSC for 12 months.

In this way, we accumulated data and obtained an all-sky
map by using 12 months of data, shown in figure 11. The red,green and blue on the map correspond to energy ranges of 0.7–
1.7 keV, 1.7–4.0 keV, and 4.0–7.0 keV, respectively. This map
was exposure-time corrected. It should be compared with thatobtained by the GSC (T. Mihara et al. in preparation).
Since the PSF of the SSC is similar to that of the GSC, theimage in figure 11 is similar to that of the GSC; however, the
SSC is sensitive to the energy range below 2 keV that can not
be reached by the GSC. The brightest sources below 2 keV are
the Cygnus Loop and the Vela SNR. The Vela SNR is also seen
to have an extent of about 7ı in diameter.
In the all-sky map, we can notice an extended structure,
particularly extended in the northern hemisphere. There are
two problems in the SSC observation. One is that the observation efficiency is about 30% due to the edge glow effect and thepassage of high background regions. The other is the observation mode of the MAXI. The MAXI is observing the sky all of
the time. We have no chance to see the dark Earth from which
we can estimate the non-X-ray background. We have the possibility that the ISS is up-side down when the space shuttle isapproaching to dock. So far, we have insufficient observation
time of the dark Earth, which makes it difficult to detect emissions from extended sources. Further observations and study
are needed to obtain an extended emission analysis extraction,
which will be reported elsewhere.
7. Conclusionmode (64-binning). The frame mode is employed in the diagnostic mode. The parallel-sum mode is employed in the standard observation mode. The detection limit (5  level) of the
SSC is 200 mCrab for one scan and 50 mCrab for one-day integration.
The frame mode shows the performance of the CCD. In thenight time, the CCD functions properly, while it suffers anedge glow when the Sun is near the FOV. The observation efficiency of the SSC is about 30%. The performance of the CCD
is continuously monitored both by the Mn-K X-rays and by
the Cu-K X-rays. In Mn-K X-rays, the energy resolution of
the CCD is 147 eV (FWHM) at the time of launch. Radiation
damage decreases the performance of the CCD. Since weemploy a charge-injection method, the degradation of the CCD
reduces to some extent. The gain of the CCD stayed almost
constant while we measured the gain decrease to be 0.9% yr1
without CI. The FWHM decreases by about 60 eV yr1 . The
recovery by the CI of the SSC is not so effective as that of
the XIS on Suzaku. Both satellites are in low-Earth orbits
with different inclination angles. The SSC passes the highbackground region at high latitude that the XIS does not reach.
Therefore, the difference in the CI may be due to the particle
background condition.
The SSC observes all of the sky by using X-ray CCDs forthe first time. There are many sources detected, not only point
sources, but extended sources. Due to the lack of an effective
observation time, we need more observation time to obtain an
extended emission analysis extraction process.

MAXI was launched in 2009 July and installed on the ISS.
Observations started from 2010 August. The CCD on the SSC
is cooled down to the working temperature of around 60ı C by
the combination of a peltier cooler, an LHP and a radiator. The
CCD is working either in a frame mode or in a parallel-sum

This work is partly supported by a Grant-in-Aid for
Scientific Research by the Ministry of Education, Culture,
Sports, Science and Technology (16002004). M. K. is supported by JSPS Research Fellowship for Young Scientists(221677).

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References
Burke, B. E., Mountain, R. W., Harrison, D. C., Bautz, M. W.,
Doty, J. P., Ricker, G. R., & Daniels, P. J. 1991, IEEE Trans.
Electron. Devices., 38, 1069
Gehrels, N., et al., 2004, ApJ, 611, 1005
Hiraga, J., Tsunemi, H., & Miyata, E. 2001, Jpn. J. Appl. Phys., 40,
1493
Katayama, H., Tomida, H., Matsuoka, M., Tsunemi, H., Miyata, E.,
Kamiyama, D., & Nemes, N. 2005, Nucl. Instrum. Methods Phys.
Res., Sect. A., A541, 350
Kirsch, M. G. F., et al. 2005, Proc. SPIE, 5898, 22
Koyama, K., et al. 2007, PASJ, 59, S23
Matsuoka, M., et al. 2009, PASJ, 61, 999
Miyata, E., et al. 2002, Jpn. J. Appl. Phys., 41, 7542
Miyata, E., et al. 2003, Jpn. J. Appl. Phys., 42, 4564
Prigozhin, G., Burke, B., Bautz, M., Kissel, S., & LaMarr, B. 2008,
IEEE Trans. Electron. Devices., 55, 2111

Strüder, L., et al. 2001, A&A,365, L18
Sugizaki, M., et al. 2010, PASJ, submitted
Sugizaki, M., Mihara, T., Kawai, N., Nakajima, M., Matsuoka, M., &the MAXI team. 2009, Astron. Telegram 2277
Tanaka, Y., Inoue, H., & Holt, S. S. 1994, PASJ, 46, L37
Tomida, H., et al. 2010, PASJ, submitted
Tomida, H., et al. 1997, PASJ, 49, 405
Tsunemi, H., Miki, M., & Miyata, E. 2004, IEEE Trans. Nucl. Sci.,
51, 2288
Tsunemi, H., Miyata, E., Ozawa, H., Matsuura, D., Tomida, H.,
Katayama, H., & Miyaguchi, K. 2007, Nucl. Instrum. Methods
Phys. Res., Sect. A., A579, 866
Turner, M. J. L., et al. 2001, A&A,365, L27
Uchiyama, H., et al. 2009, PASJ, 61, S9
Weisskopf, M. C., Brinkman, B., Canizares, C., Garmire, G.,
Murray, S., & Van Speybroeck, L. P. 2002, PASP, 114, 1