XIS QE Degradation in OrbitXIS 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

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 distribut

ed 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.

Energy

X-r

ay i

nte

ns

ity

(Assumed)Incident X-ray Spectrum

from an Object

Observed X-ray Spectrum Convolved with XIS Response

Co

un

ts/s

ec/

keV

PHA

Object

XIS Hardware

Frame Data

Data Processing Onboard DE & Ground

•Dark-level Subtraction•Event Extraction•Pulse Height (PHA) construction

Key ObjectsStable

(Incident Spectrum known)

Extended over FOV

Always Observable ?

Energy Range

Target of the contaminant study

RXJ1856 Yes (maybe)

No No 0.2-1keV Composition

E0102 Yes No Yes 0.4-3keV Evolution

Cygnus Loop Yes at somelevel

Yes No 0.2-3keV Uniformity

PK2155 No but

Smooth

No No 0.2-12keV Composition

Atmospheric F.L.

No Yes Yes 0.39keV

0.52keV

Uniformity

Evolution

RXJ1856.5-3754RXJ1856.5-3754Discovered with ROSATDiscovered with ROSATNearby (D~120pc) Isolated Neutron StarNearby (D~120pc) Isolated Neutron StarX-ray spectrum is fitted with a simple X-ray spectrum is fitted with a simple

blackbody ( against NS atmosphere model).blackbody ( against NS atmosphere model).R~4-5km Quark Star ?R~4-5km Quark Star ?

RXJ1856 Observed with Suzaku 20RXJ1856 Observed with Suzaku 2005-10/24~2605-10/24~26RMF 20051210 a-d for XIS1RMF 20051210 a-d for XIS1 Rev0.3 data -10eV offset

a: Based Cal on the Ground

b: a x excess0.15mC

c: Dead Layer =Design Value

d: c x excess0.15mC

C-K edge ~0.3keV

Suzaku/XIS ContaminationMeasurements with E0102Suzaku/XIS ContaminationMeasurements 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 Gau

ssian emission lines• Galactic + SMC absorption• pure C absorption from co

ntaminant (varabs)• gain shift -5 eV ~ -15 ev

• r2 ~ 1.6 (FIs) to 2.5 (BI)

2005-08-132005-08-312005-12-162006-01-17

OVIII NeIX NeX

MgXIOVII

2006-02-02

XIS Contamination RateXIS Contamination Rate

change in effective C column:

chip slope intercept(1016 cm-2/day)

XIS0 1.6 ±0.1 4.4 ±4.0XIS1 2.7 ±0.1 -9.6 ±15XIS2 3.1 ±0.1 -3.2 ±14XIS3 4.1 ±0.5 54. ±50.

• empirical correction for observers• contamination rate turnover (?)

• SMC NH uncertainty systematic error ±0.02 m independent of epoch

Cyg Loop

• Nearby Old Super Nova Remnant

• 2005Nov 4pointgsC-band CVI-band

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

Center Rim

NH [cm-2] 4x1020 (fix) 4x1020 (fix)

kTe [keV] 0.2 (fix) 0.2 (fix)

C [nm] 248 ±3 111 +6 -9

C Absorber thickness is about 1/2 at Rim (2005 Nov)

CenterRim

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.

DAY EARTH0 < DYE_ELV < 5

5 < DYE_ELV < 10 10 < DYE_ELV < 2020 < DYE_ELV < 30

N-K(0.39keV)

O-K(0.52keV)

Atmospheric N-K line Map XIS1(BI)

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

2005-8-13

2005-9-4 2005-10-22

2005-11-28

2005-12-24

2006-2-6

Color code is adjusted for each map

From Anabuki et al.’s poster

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

2005-8-13

2005-9-4 2005-10-22

2005-11-28

2005-12-24

2006-2-6

E0102-72

N-K lineO-K line

N-K lineO-K line

N-K lineO-K line

SN1006_NE_BGD Mrk 3

Day Earth Radial Profile(vignetting corrected,normalized by center region)

N-K lineO-K line

N-K lineO-K line

N-K lineO-K line

A2811_offset NGC 4388 MBM12_off Cloud

N-K lineO-K line

Center 6mm radius / Other area Center 6mm radius / Other area

Mean Free Path in Mean Free Path in C(2.2g/cc)C(2.2g/cc)

0.1820.182m for N-K m for N-K lineline

0.3750.375m for O-K m for O-K line 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).

Contamination Rate is Decreasing ?

N-K lineO-K line

c.r.(center) - c.r.(outer)=0.9x10-3 m/day

[Central 6mm radius count rate] / [Outer area count rate]

c.r.(outer)=1.6x10-3 m/day

c.r.(center)~ 2.5x10-3 m/day

Time(sec)

PKS2155-304XIS1(BI)

XIS3(FI)

NH(Gal)*Pow

NH(Gal)*Pow

NH(Gal)*N_C*Pow

NH(Gal)*N_C*Pow NH(Gal)*N_C*N_O*Pow

NH(Gal)*N_C*N_O*Pow

NH(Gal)=1.65e20cm~-2

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

If we assume the contaminant is DEHP…

NH(Gal)*DEHP*Pow NH(Gal)*DEHP*Pow

NH(Gal)*N_C*N_O*Pow NH(Gal)*N_C*N_O*Pow

XIS1

XIS1

XIS3

XIS3

The data may not reject the possibility of DEHP.

Assuming DEHP

Best fit C/O ratio

Nature of Contaminant:1E 0102-72.3

• 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%)

NO = 0

NC/NO= 6

Aug 05

Dec 05, Jan 06, Feb 06

Aug 05

Dec 05, Jan 06, Feb 06

Nature of Contaminant:RX J1856.5

• BI: -10 eV shiftNO / NC <0.10

FI: -3.5 eV shiftNO / NC < 0.11

FI

BI

gain fit

90% limit

0.1

1

0.2 0.3 0.4 0.5 0.6 0.7 0.80.9 1

QE model(BI;XIS1)QE model(FI;XIS2)OBF

DEHP 200nm 2.2g/ccDEHP 400nm 2.2g/ccNH=2e20

Ex(keV)

Summary• QE degradation in Suzaku XIS has been studied.• Absorber (Contaminat) thickness: XIS0<XIS1<XIS2<XIS

3• C-absorber thickness: Rim ~ 1/2 of the Center• Contamination Rate was almost constant, but there is a hin

t that the rate is decreasing recently. • Carbon is dominant in Cotaminant . There is a small contri

bution 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.