すざく」搭載X線CCDカメラ XISのSpaced

The onboard calibration for
the spaced-row charge
injection of the Suzaku XIS
Hideki Uchiyama, Yoshiaki Hyodo, Hiroya Yamaguchi, Hideyuki
Mori, Takeshi Go Tsuru, Hironori Matsumoto, Katsuji Koyama
(Kyoto Univ.), Ken'ichi Torii, Satoru Katsuda, Hiroshi Nakajima,
Kazuto Hasuike, Kiyoshi Hayashida, Hiroshi Tsunemi (Osaka Univ.),
Hiroshi Murakami, Tadayasu Dotani (ISAS/JAXA), Gregory
Prigozhin, Steve Kissel, Eric Miller, Beverly LaMarr, Mark Bautz
(MIT) and Suzaku XIS team
X-ray astronomy satellite Suzaku
& X-ray Imaging Spectrometer (XIS)


Suzaku
The 5th Japanese X-ray satellite
X-ray Imaging Spectrometer (XIS)
 X-ray CCD camera onboard
Suzaku
 3 Front Illuminated (FI) & 1 Back
Illuminated (BI) sensors
 Positional resolution
 ~2’ with X-ray telescope (HPD)
 High energy resolution
[email protected] (FWHM) in Aug.
2005 (just after launch)
 Equipped with a charge injection
(CI) structure
Suzaku satellite
CCD chip of XIS
Degradation of the energy resolution
Energy resolution (eV,FWHM)
The time dependence of the energy resolution @5.9keV
Aug. 2005
just after launch
May
2006
1.8×108
1.9×108
2×108
Time since 2000-1-1 00:00:00 (s)
The increase of charge transfer inefficiency
(CTI) causes this degradation.
How the CTI causes the degradation
ACTY
ACTX
1026 pixel
Imaging area
Q
X-ray
Q
Charge trap caused by
radiation damage in orbit
Readout charge
Frame-store region
Transfer direction
Q
Q’
Q’’
Readout node
0
Q’
ACTY
Energy
resolution
is
Q’’
degraded.
Spaced-row Charge Injection (SCI)
Charge
injection
structure
ACTY
ACTX
1026 pixel
X-ray
Q
Charge trap caused by
radiation damage in orbit
Injected charge fills the traps.
→It decreases the CTI.
54 rows
Injected
charge
Q’
Q’’
Readout node
Transfer direction
Q
Readout charge
Frame-store region
Imaging area
Q
0
Q’
ACTY
Q’’
Energy
resolution
is
recovered!

We operated XIS with the SCI technique in orbit for the first
time in August 2006 and verified the recovery of the energy
resolution from 210eV to 150eV (@5.9keV,FWHM)
Spectra of onboard cal source
55Fe
no-SCI
SCI
Mn I Kα
Mn I Kβ
Pulse height (channel)

We studied the gain non-uniformity in the SCI mode
and developed a new correction method for it.
How the SCI mitigates the gain non-uniformity

Perseus cluster of galaxies
 It is a bright diffuse X-ray source.
 It covers almost all of the FOV
of the XIS.
 Its spectrum has strong He-like
Fe Kα line and the line center is
roughly independent of the
position.
→Suitable for the study of the
gain non-uniformity over the
chip.
 Aug. 2006, in the both SCI &
no-SCI mode, exposure time
~50 kilo seconds
XIS image of
Perseus cluster
How the SCI mitigates the gain non-uniformity
Perseus cluster
ACTY
ACTX
He-like Fe
Kα
He-like Fe Kα from Perseus cluster
Pulse Height channel

Pulse Height channel
The CTI became ~30% by the SCI.
The gain non-uniformity on a smaller spatial
scale
Ground experiment of the SCI with proton-damaged
CCD
Positional dependence of Mn I Kα line
Transfer direction
Pulse Height

Tomida et al.
1997
Charge Injected row
100
200
300
400
500
Transfer pixel
“Saw-tooth” gain non-uniformity appeared.
→ Does it appear in orbit?

Onboard calibration sources 55Fe
 They
irradiate the upper
edge of XIS continuously.
→ We can use long exposure
data.
 The spectrum has Mn I Kα
line and the line center is
5.895keV.
 April 2007, in the SCI mode,
exposure time ~1 mega
seconds
XIS image of
Cal source
The gain non-uniformity on a smaller spatial
scale
Onboard
calibration source 55Fe
Charge injected row
Mn I Kα from onboard cal source
rows
C
B
A
54
Transfer
direction
Mn I Kα
Kβ
PH CH
Pulse Height channel
Charge injected row
A
B
C
Transfer
direction
ACTY
“Saw-tooth” gain non-uniformity appeared in orbit.
Correction for the gain non-uniformity
•We modeled the positional non-uniformity of the gain by
“saw-tooth” function below.
•Three parameters, the slope at ΔACTY=0, ΔACTY=54 and
PH0 specify this function uniquely.
•Fit the observed
The slope at ΔACTY=0
ACTY-PH relation
PH0
with the saw-tooth
function to obtain the
PH
the slope at
Saw-tooth
ΔACTY=0, 54 and
function
PH0, then correct the
observed PH.
The slope at
ΔACTY=54
ΔACTY
54 rows
ACTY
charge-injected rows
Saw-tooth
Correction
Result of the saw-tooth correction method
Mn I Kα from onboard cal source
Mn I Kα from onboard cal source
Pulse Height channel
fitting result of the saw-tooth function
Without Saw-tooth correction
With Saw-tooth correction
The correction reduced the gain non-uniformity at 5.9 keV from
~ 0.5% to ~ 0.1%
→The gain is uniform on the order of a few eV at 6 keV with this
correction.
 The energy resolution is also improved.
151 eV → 148 eV @5.9 keV FWHM (additional width ~ 30 eV)

The current status of the Suzaku XIS
software & data processing for the SCI
The saw-tooth correction has been built into
public Suzaku analysis software and released.
 Version 2.0 data processing incorporates the
saw-tooth correction and the calibration of the
SCI. The processing has already begun.
 The calibration database for the SCI is being
updated continuously now.

Summary





Suzaku XIS operated the spaced-row charge
injection technique for the first time and verified the
recovery of the energy resolution.
The CTI became ~30% by the SCI. The gain nonuniformity over the chip was mitigated well in orbit.
The saw-tooth gain non-uniformity was shown in
orbit in April 2007.
We developed the saw-tooth correction method. It
made the gain in the SCI mode uniform on the order
of a few eV at 6keV.
The software for the SCI mode has been released.
The data processing for the SCI mode already
started.

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