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Origin of the X-ray Spectral Variation and Seemingly Broad Iron Line

Structure in the Seyfert GalaxiesKen EBISAWA

Naoki ISO, Takehiro MIYAKAWA, Hajime INOUE

(JAXA/ISAS)

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Contents of the Talk

1. Properties of the Seyfert Galaxies2. Variable Partial Covering Model3. Explanation of the Observed Properties4. Conclusion

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1. Properties of the Seyfert Galaxies

a) Significant flux variationb) “Seemingly” broad iron-line featurec) Small variation in the iron energy band

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1a. Significant flux-variation

Suzaku observations of NGC4051 and NGC3516 (0.2—12 keV, 1bin=512sec）

Significant and aperiodic variations in various time-scales

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1b.“Seemingly” broad iron-line feature

• ASCA MCG-6-30-15

(Tanaka+ 1995)

• Looks like an iron K-line “broadened” by relativistic effects • Interpretation depends on the choice of models

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1c. Small variation in the iron energy band

• MCG-6-30-15 with ASCAEnergy dependence of Root Mean Square (RMS) variation

• The RMS spectrum drops significantly at the iron K energy band (model independent result!)

(Matsumoto+ 2003)

〜 105 sec

〜 104 sec

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Contents of the Talk

1. Properties of the Seyfert Galaxies2. Variable Partial Covering Model3. Explanation of the Observed Properties4. Conclusion

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2. Variable Partial Covering Model• Several authors have proposed idea of partial

covering for MCG-6-30-15: e.g., Matsuoka+ (1990); McKernan and Yaqoob (1998); Miller, Turner and Reeves (2008, 2009)

• We have found “double partial covering” with two different warm absorbers can explain the Suzaku MCG-6-30-15 spectra (Miyakawa, Ebisawa and Inoue 2012)

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Double partial covering

X-ray source

xspec notation: partcov(a) * exp(-NHs(x)) × partcov(a) exp(-NHs(x))

Partial covering by thick absorber with NH~1024.2cm-2 and x~101.6 and the partial covering fraction a

Partial covering by thin and more ionized absorber with NH~1022.1cm-2 and x~101.9 and the same partial covering fraction a

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2. Variable Partial Covering Model• Observed spectral variation of MCG-6-30-15 is

mostly explained by only variation of the partial covering fraction (Miyakawa, Ebisawa and Inoue 2012, PASJ, 64, 140)

• Variable Partial Covering model can explain spectral variations of other 20 Seyfert galaxies observed with Suzaku (Iso, Ebisawa+ 2013 in prep.).

11• Miyakawa, Ebisawa and Inoue (2012)

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Outer disk reflection

Direct component

Heavily absorbed component

• Double Partial covering by absorbing clouds with thick core and thin envelope. • The continuum spectrum composed of the direct component, absorbed component,

and outer-disk reflection component• Observed spectral variation is mostly explained by only change of the covering

fraction α

2. Variable Partial Covering Model

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direct component

Heavily absorbed

component

X-ray source

Ionized absorbers

Variable Partial Covering Model(Miyakawa, Ebisawa and Inoue 2012)

The X-ray luminosity of BH hardly variableGeometrical “covering fraction” is significantly variable

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Variable Partial Covering Model(Miyakawa, Ebisawa and Inoue 2012)

The X-ray luminosity of BH hardly variableGeometrical “covering fraction” is significantly variable

Covering fraction varies

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Covering fraction varies

Variable Partial Covering Model(Miyakawa, Ebisawa and Inoue 2012)

The X-ray luminosity of BH hardly variableGeometrical “covering fraction” is significantly variable

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Variable Partial Covering Model(Miyakawa, Ebisawa and Inoue 2012)

The X-ray luminosity of BH hardly variableGeometrical “covering fraction” is significantly variable

Covering fraction varies

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Variable Partial Covering Model(Miyakawa, Ebisawa and Inoue 2012)

The X-ray luminosity of BH hardly variableGeometrical “covering fraction” is significantly variable

Covering fraction varies

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Variable Partial Covering Model(Miyakawa, Ebisawa and Inoue 2012)

The X-ray luminosity of BH hardly variableGeometrical “covering fraction” is significantly variable

Covering fraction varies

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Covering fraction: Null

Variable Partial Covering Model(Miyakawa, Ebisawa and Inoue 2012)

The X-ray luminosity of BH hardly variableGeometrical “covering fraction” is significantly variable

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Contents of the Talk

1. Properties of the Seyfert Galaxies2. Variable Partial Covering Model3. Explanation of the Observed Properties4. Conclusion

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解析

Counting rateCovering fraction

Flux variation of 21 Seyfert galaxies observed withSuaku, explained by only change of the covering fraction

3. Explanation of the Observed Propertiesa. Significant flux variation

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Observed flux variations explained by “constant black hole luminosity and variable covering fraction”.

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Example of other sourcesBlack:countig rateRed:covering fraction

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Example of other sourcesBlack:countig rateRed:covering fraction

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Example of other sourcesBlack:countig rateRed:covering fraction

direct component

outer-reflection component

Heavily absorbed component

narrow ion line

The ionized iron-edge looks like a broad iron line feature

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3. Explanation of the Observed Propertiesb. “Seemingly” broad iron-line feature

Suzaku MCG-6-30-15Miyakawa, Ebisawa and Inoue (2012)

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3. Explanation of the Observed Propertiesc. Small variation in the iron energy band

• In the Variable Partial Covering model, variations of the direct component and absorbed component cancel each other

• This is most effective at the iron energy band

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3. Explanation of the Observed Propertiesc. Small variation in the iron energy band

• In the Variable Partial Covering model, variations of the direct component and absorbed component cancel each other

• This is most effective at the iron energy band

Iron linereflection

absorbed component

direct compoent

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解析

• Observed Root Mean Square spectrum is explained by only variation of the covering fraction

3. Explanation of the Observed Propertiesc. Small variation in the iron energy band

Black:dataRed:model

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Example of other sourcesBlack:dataRed:model

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Example of other sourcesBlack:dataRed:model

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Example of other sourcesBlack:dataRed:model

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Contents of the Talk

1. Properties of the Seyfert Galaxies2. Variable Partial Covering Model3. Explanation of the Observed Properties4. Conclusion

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4. Conclusion• We propose “Variable Partial Covering model” for Seyfert

Galaxies, where X-ray luminosity of the black hole is hardly variable, and the observed spectral variation is primarily due to variation of the warm absorbers in the line of sight.

• In the Variable Partial Covering model, covering fraction is the primary parameter to describe the spectral variations.

• The Variable Partial Covering model successfully explains observed spectral variations of 21 Seyfert galaxies (including MCG-6-30-15) observed with Suzaku.