Imaging Area. Frame-store Area. Hiroya Yamaguchi , Hiroshi Nakajima, Hideyuki Mori, Hironori Matsumoto, Takeshi G. Tsuru (Kyoto Univ.), Kiyoshi Hayashida, Ken ’ ichi Torii, Satoru Katsuda, Masahiro Uchino (Osaka Univ.), Dai Takei (Rikkyo Univ.), Eric Miller (MIT), and XIS team
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Hiroya Yamaguchi, Hiroshi Nakajima, Hideyuki Mori, Hironori Matsumoto,
Takeshi G. Tsuru (Kyoto Univ.), Kiyoshi Hayashida, Ken’ichi Torii, Satoru Katsuda,
Masahiro Uchino (Osaka Univ.), Dai Takei (Rikkyo Univ.), Eric Miller (MIT), and XIS team
Email(HY): email@example.comThe Onboard Calibration of XIS
Abstract: X-ray Imaging Spectrometers (XISs) are main detectors of Suzaku. They have high quantum efficiency and moderate energy resolution. Although we constructed response function for the XIS using the results of ground calibration, the performance of the XIS is gradually changing on orbit. The increase of charge transfer inefficiency (CTI) is especially remarkable, and the energy resolution and gain had been degraded as the result. Then we have been monitoring and compensated the CTI with 55Fe calibration sources which irradiate the edge of the CCD chip, and reconstructed the response function for the CTI corrected spectra. Furthermore, the XIS equips charge injection (CI) capability, which is functioning for the first time on orbit, then we can compensate the CTI column by column. We will explain our correction method using the CI capability and report the results of the correction. The change of the quantum efficiency is also confirmed on orbit, and we calibrated it using the result of the observations of Crab nebula.
3. CTI correction
CTI consists of 3 components.
Frame-store tarnsfer Cf 1024
Parallel transfer Cp Np
Serial tarnsfer Cs Ns
Performance of XIS is gradually degrading
since the launch of Suzaku due to
the radiation damage.
Q’ = Q (1-Cf)1024(1-Cp)Np(1-Cs)Ns
Q : Real PH (ADU)
Q’ : Readout PH (ADU)
Gain ～ 2%/year
ΔE ～ 50eV/year (@5.9keV)
・ CTI cannot be measured only from calibration source data.
・ Cp/Cf can be decided from diffuse source data
with strong emission line (e.g. Cygnus Loop, A426, Galactic center).
2. Charge trailing
ACTY dependence of 55Fe PH.
Before the correction.
After the correction.
・ A part of charge of each event trails to a pixel
opposite to the direction of the vertical transfer.
・ The amount of trailing charge increases
in the charge transfer process.
Time evolution of charge trailing
6.4keV line from Sgr C region.
Time evolution of CTI successfully corrected in rev0.7 and 1.2 data.
However systematic gain discrepancy (due to AE temperature?) still remains.
・ Time dependence of charge
trailing has not been considered
in XISPI process yet.
・This effect will be corrected
properly in future version of
XISPI (probably after v2.0).
Average PH (ADU)
Average PH (ADU)
Possible gain shift
in rev 0.7 and 1.2 data.
< 0.2% @ > 1keV
< 5 eV @ < 1keV
Day since launch
Day since launch
4. Energy resolution
6. Checker-flag Charge Injection
Time depending Ex-ΔE relation
Schematic view of checker-flag CI method.
・ Large column-to-column variations in
the CTI degrades the energy resolution.
・ These variations can be measured with
checker-flag CI and corrected with
・ XIS team has conducted on-orbit CI
experiment every months from 2006-05.
・ After CTI correction, energy resolution is calibrated
with 55Fe (high energy), and E0102 (low energy) data.
・ The calibration results are reflected to xisrmfgen
2006-10-17 version (utilized for rev 0.7 and 1.2 data).
・ Spaced-raw CI succeed to improve the resolution
(～200eV → ～140eV). <See Torii et al. (poster)>.
The calibration result of S-CI will be reflected to
future version of xisrmfgen.
Red: Ground calibration
(rmf provided before 20060213).
Other colors: onboard calibration.
PHA distribution of the test and reference events.
Frame image of XIS during CI experiment.
E0102 spectra fitted with old and new rmf
old rmf (20060213ver.)
new rmf (use xisrmfgen)
・ Column-to-column CTI correction significantly
reduces the “tail” component of spectra.
・ FWHM: 190 →170eV @ 5.9keV
・ These results are not reflected in rev 0.7 and
1.2 data, and will be applied in future version
of XISPI process (after rev 2.0).
・ Since Spaced-row CI method is used at present,
Checker-flag CI experiments are interrupted.
(rev 0.7 and 1.2)
5. Quantum efficiency
QE calibration with Crab data (XIS0).
・ QE at high energy is calibrated with Crab data.
・ CALDB for QE parameter was updated in xisrmfgen
2006-10-17 version (only XIS0).
・ The thickness of depletion layer of XIS0, 1, 2, and 3
are assumed as 68, 45, 70, and 66μm, respectively.
We thank to all the Suzaku SWG members and associated graduate students,
especially Y. Ishisaki, Y. Maeda, N. Ota, Y. Takei, S. Okada, and K. Suzuki.
・ QE at low energy is calibrated with E0102 data.
・ Low energy QE had been degraded by OBF
contamination <see Hayashida et al. (poster)>.
・ @ >5keV, the influence of the contamination is
Bautz M.W. et al. Proc. SPIE, 2004, 5501, 111
Koyama K. et al. PASJ, 2006, accepted
LaMarr B. et al. Proc SPIE, 2004, 5501, 385
Nakajima H. et al. 2006, in preparing