Download - The ground calibration of the back-side illuminated CCD camera of XIS onboard Astro-E2 (Suzaku)
The ground calibration of the back-side illuminated CCD camera of XIS
onboard Astro-E2 (Suzaku)
H. Yamaguchi, H. Nakajima, H. Matsumoto, T. G. Tsuru, K. Koyama (Kyoto Univ., Japan), D. Matsuura, T. Miyauchi, S.Katsuda, M. Namiki, K. Torii, K. Hayashida, H. Tsunemi (Osaka Univ., Japan), and XIS team
Contents
Introduction Characteristic of XIS-BI
Event Detection Grade method
Charge Trailing Charge trailing against the transfer.
We developed “Charge Trail Correction”.
Onboard CalibrationComparison with Chandra/ACIS
1. IntroductionSuzaku (Astro-E2)
XIS sensor
XIS : Front-illuminated (FI) CCD×3 + Back-illuminated (BI) CCD×1
BI-CCD ‥ High quantum efficiency for soft X-ray
Quantum efficiency of XIS
XIS-FIXIS-BI
X-ray
electrode
1. Introduction
Chemisorptioncharging process
strengthen the electric field
Collection efficiency ofelectrons were improved !!
structure of XIS-BI
back surface
spread
Charge cloud spreads widely↓
Energy resolution become worse
ex. Chandra/ACISΔE(BI) 2×ΔE(FI)≒
1. Introduction
Energy resolution of the XIS-BI is almost comparable with FI!
ΔE= 49eV (BI) 42eV (FI) @0.53keV
ΔE= 129eV (BI) 128eV (FI) @5.9keV
cou
nts/
keV
Spectrum of O-K line
XIS-BIXIS-FI
Components Location X-ray Source QE reference
Chip level CSR/MITFluorescent X-rays (C,O,F,Al,Si,P,Ti,Mn,Cu)
ACIS chips calibrated at BESSY
Camera without OBF
+Flight Model AE
Osaka Univ.Grating Spectrometer
0.2-2.2keVPolypro-window Gas PC & XIS-EU
Kyoto Univ.Fluorescent X-rays (Al,Cl,Ti,Mn,Fe,Zn,Se)
Window-less SSD
OBFSynchrotron Facility
Synchrotron X-rays + monochrometer
(Transmission measurement with PIN diode)
Camera onboard the satellite
ISAS/JAXA 55Fe
1. IntroductionGround Calibration Task ShareGround Calibration Task Share
2. Event DetectionGrade02346 are used as X-ray event
The center pixel
A pixel whose PH is larger than split threshold and added to the PHA (= summed PH)
A pixel whose PH is larger than split threshold but NOT added to the PHA
Grade0
Grade1
Grade2
Grade3
Grade4
Grade5
Grade6
Grade7
split over 2x2 region
We analyzed BI data similarly to FI.↓
Several problems were found.
3. Charge TrailingV
erti
cal Imaging Area
of XIS
Uniform illumination of fluorescent X-ray
Read out node
Distribution of Grade0,2,3,4,6 events
V (Vertical)
Cou
nts
Distribution of Grade7 events
Cou
nts
V (Vertical)
not uniform!
Ground Calibration
transfer
Several X-ray events escape to Grade7?
3. Charge Trailing
transfer transfer transfer
Trailing charge
Some charges are deposited during the transfer.
Grade0 Grade2
Ver
tica
lContribute to the increasing
Grade0 Grade2
PH
3. Charge Trailing
transfer transfer transfer
Trailing chargeGrade6 Grade7
Distribution of Grade7 events
Cou
nts
V (Vertical)
PH
3. Charge Trailing
Q
’ (A
DU
)
extracted only Mn-K event
CTR = 4.5×10-6 @5.9keV (Mn-K)
“Charge Trail Ratio” (CTR) ≡ the probability of charge trailing par 1 pixel transfer
N (Number of transfer)
V
Trailing Charge ≡ Q’[ADU]
Q’ = C×NQ’ = C×N ; C = 6.8×10-3
Mean PHA ≡ Q[ADU]
spectrum of Mn-K
CTR [1/transfer] = C/Q
3. Charge Trailing
C
TR
Q (PHA)
CTR depends on the PHA of event
Relation of the CTR and the PHA is able to be expressed by the power-law function
CTR = (1.72×10-4)×(PHA[ADU])-0.5
We have developed “Charge Trail Correction”.
Before AfterV V
3. Charge TrailingAfter the Charge Trail Correction …
Distribution of Grade0,2,3,4,6 events
not uniform!
Cou
nts
V (Vertical)
Distribution of Grade0,2,3,4,6 events becomes uniformly.Grade7 events due to charge trail are successfully reduced.
→ The detection efficiency improve about The detection efficiency improve about 10-20%.10-20%.
4. Spilt Threshold OptimizationSplit threshold = 20ADU (for XIS-FI)
XIS-FI (SpTh.= 20ADU)
XIS-BI (SpTh.= 20ADU)
20ADU is not optimum value of the split threshold for BI?
O-K line
Zn-K lineoptimum split threshold
Split Threshold (ADU) Split Threshold (ADU)
Split Threshold (ADU)
ΔE (eV)
Efficiency
O-K (0.5keV) Zn-K (8.6keV)
4. Spilt Threshold Optimization
10ADU for 0.5keV13ADU for 8.6keV
4. Spilt Threshold Optimization
The function for setting split threshold optimum split threshold [ADU] = 10.359 + 2.2075 log10(E [keV] )
Optimize the split threshold for each energy events
we make Grade classification using variable split threshold
XIS-FI (SpTh.= 20ADU)
XIS-BI (SpTh.= 20ADU)
XIS-BI (variable SpTh.)
Energy resolution of the XIS-BI is almost comparable with FI
ΔE= 49eV (BI) 42eV (FI) @0.53keV
ΔE= 129eV (BI) 128eV (FI) @5.9keV
5. Onboard Calibration
XIS FIXIS BI
XIS keeps their performance even after the launch!!
ACIS BI
Spectra of E0102-72
Summary Suzaku/XIS is composed of 3 FI-CCD and 1 B
I-CCD. Good energy resolution of BI was achieved by
chemisorption charging process. We developed new analysis method, “Charge
Trail Correction”. → Detection efficiency improved. More detailed onboard calibration is proceedin
g now.