1. IACHEC 2019@Shonan International Village
The spectral response of X-ray CCDs in the energy band around Si-K edge: a solution to the Si-K edge problem for the XIS onboard Suzaku
Kiyoshi HAYASHIDA, Koki OKAZAKI , Riku SHOMURA, Tomokage YONEYAMA, Hironori MATSUMOTO, Hirofumi Noda, Hiroshi TSUNEMI (Osaka Univ.), Hiroshi NAKAJIMA(Kanto-Gakuin Univ.), Koji MORI (Univ. of Miyazaki), Masahiro TSUJIMOTO, Yoshitomo MAEDA, Ken EBISAWA (ISAS/JAXA)
Today I’d like to talk about “The spectral response of X-ray CCDs in the energy band around Si-K edge: a solution to the Si-K edge problem for the XIS onboard Suzaku.”　Most of the contents were described in SPIE proceeding by Okazaki et al. but I include recent progress.
See also Okazaki et al. , SPIE Proc , id F (2018)
May 20th, 2019
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2. IACHEC 2019@Shonan International Village
Outline
Introduction
Suzaku and XIS
Si-K edge problem
Solution of the Si-K edge problem
Introduce discontinuity in PH_peak-Ex relation
Application to several targets
Discussion
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3. The X-ray Astronomy Satellite “Suzaku”
X-ray CCD Cameras
“X-ray Imaging Spectrometers
(XIS)”
FI-CCD × 3 (XIS0, 2,3)
BI-CCD × 1 (XIS1)
Suzaku launched on 2005, and operated 10 years in orbit.
4 X-ray CCD cameras onboard are XIS. 3 of 4, XIS0, 2 and 3 employ an FI-CCD and the other XIS1 does BI-CCD.
(JAXA)
(Koyama et al. 2007)
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4. Two Types of CCDs Soft X-ray Hard X-ray Soft X-ray Hard X-ray
electrode
Insulation layer
depletion layer
~42um
depletion layer
~65um
Insulation layer
You know FI and BI CCDs.
electrode
FI (Front-Illuminated)-CCD
XIS0, XIS2, XIS3
BI (Back-Illuminated)-CCD
XIS1
Note: XIS2 was stopped on 2006
XISs were sensitive in keV
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5. IACHEC 2019@Shonan International Village
Si-K Edge Problem
LMC X-3 (Black Hole Binary)
model: phabs*(diskbb + powerlaw)
black: FI-CCD
red: BI-CCD
ratio= data model
about 10 % residual around Si-K edge (1.839 keV)
different
direction
peak energy
We had a response/calibration problems around Si-K edge. About 10% residua;. Different direction between FI and BI. The peak energy is also different.
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6. Si-K Band was ignored in the analysis
In some papers, Si-K band were ignored. That’s not good.
Perseus Cluster (Tamura et al. 2009)
RX J (Ota et al. 2008)
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7. IACHEC 2019@Shonan International Village
Response Matrix
𝑆 𝑃𝐼[0] 𝑆 𝑃𝐼[1] ⋮ ⋮ 𝑆 𝑃𝐼[𝑛−1] = 𝑅 0,0 𝑅 0,1 … 𝑅 0,𝑚−1 𝑅 1,0 𝑅 1, ⋮ 𝑅 𝑛−1, 𝑅 𝑛−1,𝑚− 𝑀 𝐸[0] 𝑀 𝐸[1] ⋮ ⋮ 𝑀 𝐸[𝑚−1]
PI spectrum
incident X-ray energy spectrum
response matrix
You all are familar with reseponse matrix. For XIS, xisrmgen is the software to make the response.
The software “xisrmfgen” makes response matrixes for XIS.
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8. IACHEC 2019@Shonan International Village
PI_peak-Ex Relation
PI_peak:
peak PI when a monochrome X-ray enters CCD
Ex: incident X-ray energy
assumed 𝑃𝐼_𝑝𝑒𝑎𝑘 channel = 𝐸 x eV [eV/channel]
response matrix
Ex (keV)
4095
PI_peak [channel]
PI(channel)
So far, in xisrmfgen, PI_peak is assumed to be proportional to the incident X-ray energy Ex. So PI peak gets in a diagonal line in the matrix.
PI_peak
get in a diagonal line
Ex [keV]
Si_Kedge=1.839
14.95
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9. Introduce New Parameters in PI_peak-Ex relation
response matrix
Ex (keV)
jnct_hiene
4095
PI_peak [channel]
jmp_hiene
PI(channel)
This time, we introduced a jump between PI peak Ex relation. We should have noticed before but.
We intoudced three parameters, jmp loene, lump hienem and junction hiene, the last one fixed to be 5.9keV because we don’t want to touch the gain primarily calibrated at 5.9keV.
jmp_loene
PI_peak
is discontinuous
jmp: gap from the original linear relation at Si-K edge
junct: the energy where the relation returns original
5.9
Ex [keV]
Si_Kedge=1.839
14.95
(default)
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10. Search for Best Jump Values
Calibration target : LMC X-3 (black hole binary)
Use model: phabs*(diskbb + powerlaw)
Fit in keV
Fix 𝑁 𝐻 and Γ
Refit in keV
search the jump values which make reduced-chi square ( 𝜒 𝑟 2 ) minimum
Search Range (step 0.1 channel)
XIS0
XIS3
XIS1
jmp_loene [channel] − − − −
We then searched the jump values that minimize the chi square value with LMC X-3 data.
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11. Best Jump Values for XIS0 (FI)
2.5
black: response without jump
𝜒 𝑟 2 = for 297 d.o.f
red: response with jump
jmp_loene=+0.7, jmp_hiene=+4.9
𝜒 𝑟 2 = for 297 d.o.f
This is one example. Black data points is fitted either with reseponse without jump and wth jump. You can clearly see the improvement.
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12. Best Jump Values for XIS3 (FI)
black: response without jump
𝜒 𝑟 2 = for 297 d.o.f
red: response with jump
jmp_loene=+0.2, jmp_hiene=+4.2
𝜒 𝑟 2 = for 297 d.o.f
This is for XIS3, another FI
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13. Best Jump Values for XIS1 (BI)
black: response without jump
𝜒 𝑟 2 = for 297 d.o.f
red: response with jump
jmp_loene=−1.0, jmp_hiene=−4.1
𝜒 𝑟 2 = for 297 d.o.f
This is XIS1, BI case. We found the improvement, but not as good as FI case.
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14. Summary of Best Jump Values
jmp_loene
[channel]
jmp_hiene
𝝌 𝒓 𝟐
[for 297 d.o.f]
without jump
XIS0
(FI)
+0.7
+4.9
1.1468
2.3159
XIS3
+0.2
+4.2
1.1046
2.2799
XIS1
(BI)
−1.0
−4.1
1.7205
2.6515
This table summarize the best jump values. For all sensor, reduced-chi2s were improved by about 1. Jump direction is positive and negative for FI abd BI respectively.
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15. IACHEC 2019@Shonan International Village
Perseus Cluster (XIS0)
w/o jump -> “before”
w/ jump -> “after”
model : phabs*(vapec1 + vapec2 + powerlaw)
before
after
𝜒 𝑟 2 = for 2060 d.o.f
𝜒 𝑟 2 = for 2060 d.o.f
We also applied the reseponse with jump to other sources, this case Perseus cluster. You see the improement.
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16. IACHEC 2019@Shonan International Village
PKS (XIS0)
NOT set jump -> “before” set jump -> “after”
model : phabs*logpar
!!! We fitted in keV and zoomed keV
2005
2014
before/after
before/after
reduced-chi square
for 296 d.o.f
for 296 d.o.f
reduced-chi square
for 296 d.o.f
for 296 d.o.f
This is another example, PKS2155 observed in different epoch.
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17. X-ray Attenuation Length in Silicon
The attenuation length is discontinuous at Si-K edge( eV)
14.3 𝜇m at eV (= 𝐸 below )
1.3 𝜇m at eV (= 𝐸 above )
Let us consider possible origin of this jump. We think the key should be in the jump in the attenuation length in siilion. 14.3micrometer below the edge and 1.3 micrometer above the edge.
The path length of the electron cloud changes discontinuously at Si-K edge. (
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18. jump = jmp_hiene –jmp_loene
Summary of Jump
jmp_loene
[channel]
jmp_hiene
jump = jmp_hiene –jmp_loene
[eV]
XIS0
(FI)
+0.7
+4.9
4.2 15
XIS3
+0.2
+4.2
4.0
XIS1
(BI)
−1.0
−4.1
−3.1
−11
This is the summary of jump again.
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19. Possible Origin of Jumps
※Si-K edge : eV
𝐸 below : eV
𝐸 above : eV
Possible Origin of Jumps
The longer the path length is, the larger the charge loss is.
Some amount of charges is lost in the depletion layer?
PI_peak
PI_peak Ex Ex
𝐸 below
𝐸 above
BI-CCD
FI-CCD
𝐸 below
𝐸 above
X-ray
X-ray
electrode
1.3 𝜇m
1.3 𝜇m
depletion
layer
1.3 𝜇m
Schematically PI_Peak Ex relation is illustrated like this for FI and BI.
X-ray absorption depth is different like this. The charge have to travel with a distance illustrated with green arrows. f we assume some charges are lost in their travel, and the longer the path is the lager the loss is.
We can explain the jumps qualitatively.
14.4 𝜇m
14.4 𝜇m
42 𝜇m
14.4 𝜇m
65 𝜇m
40.7 𝜇m
27.6 𝜇m
depletion layer
electrode
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20. Conclusion (until Okazalo et al. SPIE proc 2018 and HEASOFT v6.25)
Introduction of “jump” in response PI_peak-Ex relation, the residual around Si-K edge was reduced.
Jump parameters were determined by fitting LMC X-3.
The reduction of the residual was confirmed also for other targets; Perseus Cluster with emission lines, PKS2155 observed a few times.
Jumps are ∼4 channel (15 eV) for XIS0 and 3, and ∼−3 channel (11 eV).
We speculate some amount of charges is lost in the depletion layer; the longer the path length is, the larger the charge loss is.
“xisrmfgen” in which jumps are implemented with their optimized values was released on Oct as a part of HEASOFT v6.25.
Here is the summary. The revised xisrmfgen and its default jump were released in HEAsoft v6.25 last year.
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21. Further Optimization after HEASOFT v6.25
Jump values are tuned also with M87 and Perseus Cluster in which line emissions are present.
However, significant residual remains for the BI.
LMC X-3 (XIS1)
red: response w/ jump
jump=−2.8 channel
𝜒 𝜈 2 =1.72 for 297 d.o.f
in V6.25
after
loene (ch)
hiene (ch)
XIS0
+0.2
+4.5
-1.9
2.4
XIS1
-2.0
-4.7
-0.1
-2.9
We have tried further optimization after that. Jump values are tuned with other sources. Altough amount of jump are the same, absolute energy scale is different. Even after this, we found the residual is relatively larger for BI.
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22. Further Optimization after HEASOFT v6.25
LMC X-3 (BH Binary)
QE of BI-CCD is reconsidered.
red: w/o edge model
𝜒 𝜈 2 =1.72 for 297 d.o.f
purple: w/ edge model
𝜒 𝜈 2 =1. 16 for 297 d.o.f
Au-M
BI surface design
Si-K
Hf-M
Hf O 2 (5 nm)
Si O 2 (3 nm)
Si Depletion Layer
Ag (1 nm)
HfO2: 4nm
SiO2+Si deadlayer:
160nm
We then reconsidered the QE, in particular the surface dead layer of the BI CCD. Tuning some values from its design values, we can improve the fit. We are considering update of the CALDB describing the QE.
1.4
1.6
1.8 2
2.2
2.4
Energy (keV)
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23. IACHEC 2019@Shonan International Village
For XRISM Xtend
Response generator is being updated from that for Hitomi SXI so as to implement possible jumps in the Ex – PI_peak relation.
Note: PH->PI conversion should not have jumps. We need matrices to implement a jump.
Experiments around Si-K edge performed with a test CCD before the Hitomi launch have been investigated in detail.
Irradiation of continuum X-rays are considered.
This is the final slide. The XRISM Xtend CCD has different design from XIS and we have not yet concluded similar jump is needed or not. But, we introduce a function to implement possible jumps in the software, at least
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24. IACHEC 2019@Shonan International Village
Backup Slide
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25. XIS Experiments on Ground with a Grating
Gaussian Fit (Response Profile is NOT taken into account)
W-M line contamination makes analysis around Si-K edge difficult
FM Spare FI0
FM Spare BI1
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26. Application to Cluster and SNR Spectra
Tycho (SNR)
Perseus Cluster
𝜒 𝜈 2 =5.06 for 284 d.o.f
𝜒 𝜈 2 =1. 72 for 284 d.o.f
𝜒 𝜈 2 =22.91 for 272 d.o.f
𝜒 𝜈 2 =27.53 for 272 d.o.f
model: phabs*(vapec*2 +PL)
(Tamaru+2009)
model: phabs*(vnei*3 + PL
+Gaussian) (Katsuda+2015)
左がペルセウス座銀河団、右が超新星残骸Tychoでのフィッティング結果です。SNRではgaussianの輝線の速度分散を考慮しています。ここまでと同様同一のデータに対し、ジャンプ無しの応答行列用いた結果が青、ジャンプ有りの応答行列を用いた結果が赤になります。銀河団では、ジャンプ導入により最大で15%程度あった残差が5%以下にまで改善されました。一方、SNRでは改善したキャリブレーション精度を大きく超えた残差が残りました。
1.4
1.6
1.8 2
2.2
2.4
1.4
1.6
1.8 2
2.2
2.4
Energy (keV)
Energy (keV)
We need to Update Emission model for this case.
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27. Study of Si-K edge response in 1994
Theory (Fraser et al., NIMA, 1994)
W-value jump by +0.2%
Experiment (Owens et al., NIMA, 1994)
W-value jump by +0.5%