1. XIS QE Degradation in Orbit XIS Review2006 Mar 10
K. Hayashida, E.Miller, N. Anabuki,
S. Katsuda, K. Torii, H. Tsunemi (Osaka Univ),
H. Matsumoto (Kyoto Univ.), A.Bamba (Riken),
M. Kokubun (Tokyo Univ.) and the SUZAKU XIS team

2. Outline of the Problem Findings
Some of the observed spectra at low energy (<1keV) were not what we expected
According to the knowledge from previous missions.
Inconsistent among the XIS 4 sensors
QE degradation at low energy is explained by introducing extra carbon absorber in the XIS response (~2005Dec). Contamination is most likely cause.
We performed repeated observations of one source (E0102). Evolution of the QE degradation was found.
XIS response in which extra carbon absorber was prepared and distributed to SWG members and GOs, with empirical model of its time evolution.
Analysis of diffuse sources indicated nonuniformity of the carbon absorber within XIS FOV. Contamination on OBF is most likely cause.
Analysis of atmospheric fluorescent line provided further data for time evolution and nonuniformity.
Detailed spectrum analysis of some sources provided information on the composition of the absorber.

3. Dark-level Subtraction Event Extraction
(Assumed)
Incident X-ray Spectrum from an Object
XIS Hardware
X-ray intensity
Frame Data
Object
Energy
Observed X-ray Spectrum
Convolved with XIS Response
Data Processing
Onboard DE & Ground
Observed X-ray spectrum is compared with assumed incident spectra convolved with the XIS response.
Dark-level Subtraction
Event Extraction
Pulse Height (PHA) construction
Counts/sec/keV
PHA

4. Key Objects Stable (Incident Spectrum known) Extended over FOV
Always Observable ?
Energy Range
Target of the contaminant study
RXJ1856
Yes (maybe) No
0.2-1keV
Composition
E0102
Yes
0.4-3keV
Evolution
Cygnus Loop
Yes at somelevel
0.2-3keV
Uniformity
PK2155
No but
Smooth
0.2-12keV
Atmospheric F.L.
0.39keV
0.52keV

5. RXJ1856.5-3754 Discovered with ROSAT
Nearby (D~120pc) Isolated Neutron Star
X-ray spectrum is fitted with a simple blackbody ( against NS atmosphere model).
R~4-5km Quark Star ?

7. RXJ1856 Observed with Suzaku 2005-10/24~26 RMF 20051210 a-d for XIS1
Rev0.3 data -10eV offset
C-K edge ~0.3keV
a: Based Cal on the Ground
b: a x excess0.15mmC
c: Dead Layer =Design Value
d: c x excess0.15mmC

8. Suzaku/XIS Contamination Measurements with E0102
E0102: SNR in SMC, bright in soft X-ray lines
excellent calibrator for low-E gain, QE changes
contamination degrading low-E eff. area of all XIS’s
model
thermal bremss + 24 Gaussian emission lines
Galactic + SMC absorption
pure C absorption from contaminant (varabs)
gain shift -5 eV ~ -15 ev
r2 ~ 1.6 (FIs) to 2.5 (BI)
OVIII
NeIX
NeX
OVII
MgXI

9. XIS Contamination Rate
empirical correction for observers
contamination rate turnover (?)
SMC NH uncertainty  systematic error ±0.02 m independent of epoch
change in effective C column:
chip slope intercept
(1016 cm-2/day)
XIS0 1.6 ± ±4.0
XIS1 2.7 ± ±15
XIS2 3.1 ± ±14
XIS3 4.1 ± ±50.

10. Cyg Loop Nearby Old Super Nova Remnant 2005Nov 4pointgs C-band
CVI-band

11. C-band/CVI-band map in detector coordinate =Inidicating absorber thickness is not uniform

12. C Absorber thickness is about 1/2 at Rim (2005 Nov)
Center
Rim
Center
Rim
NH [cm-2]
4x1020 (fix)
kTe [keV]
0.2 (fix)
C [nm]
248 ±3
C Absorber thickness is about 1/2 at Rim (2005 Nov)

13. Atmospheric Fluorescence Line
When the telescope is looking at the shining Earth or its atmosphere, fluorescence lines of the Earth atmosphere (N-K, O-K) by Solar X-rays are contaminated in the observed spectra.
Intensity and line ratio depends on the elevation angle from the Earth rim and the Solar activity.
N-K
(0.39keV)
O-K
(0.52keV)
DAY EARTH
0 < DYE_ELV < 5
5 < DYE_ELV < 10
10 < DYE_ELV < 20
20 < DYE_ELV < 30

14. Atmospheric N-K line Map XIS1(BI)
From Anabuki et al.’s poster
Color code is adjusted for each map
N-K line
Day Earth
0 < DYE_ELV < 5
5 < DYE_ELV < 10
10 < DYE_ELV < 15
15 < DYE_ELV < 20
20 < DYE_ELV < 25

15. Atmospheric O-K line Map XIS1(BI)
0 < DYE_ELV < 5
Day Earth
5 < DYE_ELV < 10
10 < DYE_ELV < 15
15 < DYE_ELV < 20
20 < DYE_ELV < 25

16. Day Earth Radial Profile (vignetting corrected,normalized by center region)
N-K line
O-K line
SN1006_NE_BGD
Mrk 3
N-K line
O-K line
A2811_offset
NGC 4388
MBM12_off Cloud

17. Center 6mm radius / Other area
N-K line
O-K line
Mean Free Path in C(2.2g/cc)
0.182mm for N-K line
0.375mm for O-K line
Spatial Difference in Carbon contamination thickness can be modeled with Atmospheric N-K, O-K data.
Thickness at the center is evaluated by E0102 and RXJ1856 obs.
Thickness (t,detx,dety) will be modeled/introduced in arfbuilder (or rmfbuilder).

18. Contamination Rate is Decreasing ?
N-K line
O-K line
[Central 6mm radius count rate] / [Outer area count rate]
c.r.(center) - c.r.(outer)=0.9x10-3 mm/day
c.r.(center)~ 2.5x10-3 mm/day
c.r.(outer)=1.6x10-3 mm/day
Time(sec)

19. PKS2155-304 XIS1(BI) NH(Gal)*Pow NH(Gal)*N_C*Pow NH(Gal)*N_C*N_O*Pow
NH(Gal)=1.65e20cm~-2
XIS1(BI)
NH(Gal)*Pow
NH(Gal)*N_C*Pow
NH(Gal)*N_C*N_O*Pow
XIS3(FI)
NH(Gal)*Pow
NH(Gal)*N_C*Pow
NH(Gal)*N_C*N_O*Pow

20. N_C vs N_O XIS1(BI) XIS3(FI) N_C(1e18cm^-2) 2.4+/-0.030 4.4+/-0.098
N_O(1e17cm^-2)
1.4+/-0.29
5.4+/-0.55
N_O/N_C
0.059+/-0.012
0.12+/-0.013
Cf DEHP(C24H38O4) N_O/N_C=1/6=0.17

21. If we assume the contaminant is DEHP…
XIS1
XIS3
Assuming DEHP
NH(Gal)*DEHP*Pow
NH(Gal)*DEHP*Pow
XIS1
XIS3
Best fit C/O ratio
NH(Gal)*N_C*N_O*Pow
NH(Gal)*N_C*N_O*Pow
The data may not reject the possibility of DEHP.

22. Nature of Contaminant: 1E 0102-72.3
NO = 0
Aug 05
Dec 05, Jan 06, Feb 06
BI residuals change with time
Aug 2005
~ no contamination
Dec 2005 and later
excess absorption in model below 0.5 keV
too much C, adding O improves residuals
formally: NO/Nc < 0.2 (90%)
NC/NO= 6
Aug 05
Dec 05, Jan 06, Feb 06

23. Nature of Contaminant:RX J1856.5
gain fit BI FI
BI: -10 eV shift NO / NC <0.10 FI: eV shift NO / NC < 0.11
90% limit

25. Summary QE degradation in Suzaku XIS has been studied.
Absorber (Contaminat) thickness: XIS0<XIS1<XIS2<XIS3
C-absorber thickness: Rim ~ 1/2 of the Center
Contamination Rate was almost constant, but there is a hint that the rate is decreasing recently.
Carbon is dominant in Cotaminant . There is a small contribution of O; N_O/N_C <0.13, which is smaller than DEHP value of 0.17, but we need to consider systematic error of response models before concluding the contaminant is pure DEHP or not.
RXJ1856 observation in this March will help it
Modeling the QE degradation is in progress with E0102 data and atmospheric N-K line data. Promising at least for BI-CCD (XIS1) so far. However, low energy band will be unavailable if the QE degradation continues.