10.10.121 High Energy View of Accreting Objects: AGN and X-ray Binaries

Geometrical Configuration of Accretion Flows in Cyg X-1

in the Low/Hard State with Suzaku

Shunsuke Torii (The University of Tokyo) Kazuo MakishimaUT, Shin’ya YamadaUT, Kazuhiro NakazawaUT, Chris Done (University of Durham)

1. Low/Hard State Pictures

12.10.102

Emission mechanism:

Thermal Comptonization Geometry:

A cool disk and a hot corona

Zdziarski+ 2004

What supplies seed photons to the Comptonizing corona? What is the geometry of the disk and the corona like? What is the origin of fast time variability?

High Energy View of Accreting Objects: AGN and X-ray Binaries

Still unknown are

Suzaku

2-1. Suzaku Results on Cyg X-1: Time Averaged Spectra

12.10.103 High Energy View of Accreting Objects: AGN and X-ray Binaries

(Makishima+ 2008)

Energy (keV) χ2 = 1.13 (349)

νFν spectrum of Cygnus X-1 νFν spectrum of Cygnus X-1

χ2=1.13(349)

Hot corona(xspec compPS)– Hard optical depth ~ 1.5 　 – Soft opt. dep. ~ 0.4Te ~ 100 keV, Rseed ~ 210 km

Directly visible cool disk– Tin ~ 0.2 keV, Rin ~ 250 km

Weakly broadened Iron line– EC 6.3 keV, EW 290 eV– Sigma ~ 1 keV (consistent with 15

Rg) Reflection from the disk

– Omega / 2π ~ 0.4

The disk is truncated at √Rseed 2+ Rin 2 ~ 15 Rg

Suzaku observation in the Low/Hard State, total exposure of 17 ks

4 High Energy View of Accreting Objects: AGN and X-ray Binaries

2-2: Intensity Sorted Spectra

Sort events by XIS count rates into high or low on a time scale of 1 s

Ave.

1 s bin

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5 High Energy View of Accreting Objects: AGN and X-ray Binaries

The corona− Seed photons− y-parameter

The disk− Tin

− Rin

Fe-K line− EW

Reflection solid angle− Ω/2π

High eventsLow events From low to high

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2-2: Intensity Sorted Spectra

Disk unchanged!

A cool disk and a hot corona of two optical depth Inner disk radius is ~15 Rg (consistent with Fe-K line width)

The disk penetrates halfway into the corona (moderate reflection) When the source flares up, the disk remains constant while seed

photon increases and y-parameter decreases

6 High Energy View of Accreting Objects: AGN and X-ray Binaries

2-3: Interpretation from a Single Suzaku Observation

inhomogeneous corona

cool disk BH

reflection raw disc ComptonWhen XIS count rate is low Corona has many holes

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A cool disk and a hot corona of two optical depth Inner disk radius is ~15 Rg (consistent with Fe-K line width)

The disk penetrates halfway into the corona (moderate reflection) When the source flares up, the disk remains constant while seed

photon increases and y-parameter decreases

7 High Energy View of Accreting Objects: AGN and X-ray Binaries

inhomogeneous corona

cool disk BH

reflection raw disc ComptonWhen XIS count rate is highDisk coverage may increase?

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2-3: Interpretation from a Single Suzaku Observation

3-1:Further 24 Observations of Cyg X-1 with Suzaku

25 observations−Low/Hard State−With various intensity

Use RXTE ASM count (CASM) as a soft X-ray flux indicator

8

● Suzaku Observation

0 60RXTE ASM (1.5-12 keV) count rate (s-1)

0

2

Har

dnes

s (5

-12

keV

/1.5

-3 k

eV)

High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10

3-2: Three Representative Spectra: (1) XIS + HXD

→ Concentrating on hard X-raysHigh Energy View of Accreting Objects: AGN and X-ray Binaries9 12.10.10

Cutoff energy appears to be decreasing

Hard X-ray slope (high-τ Compton) softens

Contribution from a cool disk appears to be increasing

Low-τ Compton component increases

10

PIN GSOCASM=14.9 cts/s CASM=23.3 cts/s CASM=45.0 cts/s

χ2/dof =146/134 153/135

High Energy View of Accreting Objects: AGN and X-ray Binaries

The three spectra were reproduced with a single Compton component The fit quantifies the inferences of the previous slide

3-3: Three Representative Spectra: (2) compPS Fit

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soft X-ray flux photon index cutoff energy ?

The fit was successful on the remaining data sets

reflection

140/135

y= 1.39Te= 76 keVΩ/2π= 0.25

y= 1.26Te= 85 keVΩ/2π= 0.33

y= 1.00Te= 78 keVΩ/2π= 0.39

3-4: Compton y-parameter vs. ASM count

y-parameter decreases from 1.4 to 1.0 when ASM count

increases by a factor of 3 Cannot distinguish whether

Te or τ decreases

11

y ∝ Te×τ Te

τ

High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10

3-5: Reflection vs. ASM count

Reflection solid angle increases by ~30% when CASM triples

Gilfanov+ (1999), Zdziarski+ (2000), Ibragimov+ (2005) 12

Ω/2π

High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10

4-1: Power Spectral Density vs. ASM count

When CASM increases by a factor of 3,

time scale of variability ν∝ b-1

low frequency power

decreases by an order of magnitude13

PIN data (10-60 keV)50 ms bin 409.6 s/interval

Break frequency (νb)

Low frequency power (from 0 to 0.01 Hz)

High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10

4-1: Power Spectral Density vs. ASM count

When CASM increases by a factor of 3,

time scale of variability ν∝ b-1

low frequency power

decreases by an order of magnitude14

PIN data (10-60 keV)50 ms bin 409.6 s/interval

Break frequency (νb)

Low frequency power (from 0 to 0.01 Hz)

High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10

νPν

4-2: Energy Dependence of Time Variability

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Auto correlation of 4 bands Cross correlation with 10-20 keV

Higher energy bands show narrower peaks (faster variability) Correlations are all peaked at 0.0 +/− 0.1 s Higher energy bands show more asymmetric form, with harder

photons lagging to softer ones (see especially 100-200 keV one)

High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10

0.1 s bin 409.6 s/interval

5-1: Discussion on Mass Accretion FluctuationWhen mass accretion rate( C∝ ASM) increases

−Variation time scale shortens, low frequency power decreases Outer radius of the corona decreases−Reflection solid angle increases The disk intrudes into the corona more deeply−y decreases Increased seed photons degrade Comptonization efficiency

16 High Energy View of Accreting Objects: AGN and X-ray Binaries

Corona BH

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As energy gets higher−Variation time scale becomes shorter In higher energies, photons are emitted closer to BH−The hard lag becomes clearer Accreting matter falling in a viscous time scale of ~ 1 sec.

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5-2:Discussion on Energy Dependence of Time Variability

High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10

hotter region

As energy gets higher−Variation time scale becomes shorter In higher energies, photons are emitted closer to BH−The hard lag becomes clearer Accreting matter falling in a viscous time scale of ~ 1 sec.

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5-2:Discussion on Energy Dependence of Time Variability

High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10

hotter region

Accreting blob

As energy gets higher−Variation time scale becomes shorter In higher energies, photons are emitted closer to BH−The hard lag becomes clearer Accreting matter falling in a viscous time scale of ~ 1 sec.

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5-2:Discussion on Energy Dependence of Time Variability

High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10

hotter region

Accreting blob

6: Summary

We analyzed 25 Suzaku observations of Cyg X-1.

As mass accretion rate increases, reflection solid angle increases and y, break frequency and low frequency power decrease.

Above can be explained by decreasing outer radius of the corona and deeper penetration of the accretion disk into the corona.

Higher energy photons vary more rapidly and have delayed components, compared to softer ones.

Energy dependence of time variability can be explained by taking into account falling time of accreting matter.

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Deeper Analysis of Asymmetry in CCF

Parameterize hard lags by taking area ratios (B/A > 1)Hard lags become more significant in softer observations?

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Appendix

- 1

B/A - 1

A B

t = 0

Lag in higher energy (s)

Chris and UT Model for a Hard Lag Behavior

Extent of a hard lag depends on low-τ componentNew insight for approaching a corona-disk geometry?

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Corona BH

Geometry Energy spectraHXDHarder obs

Softer obs

High-τ dominant.Less asymmetric

Low-τ invades.More asymmetric

In the HXD regionLow-τ

High-τ

Supplement : PSD and ACF Power spectral density (PSD) and auto correlation function

(ACF) are Fourier conjugate, i.e. equivalent to each other PSD has frequency domain while ACF has time domain Time scale of variability in BHB appeared as a break in PSD

while it appears as decay time of correlation in ACF Faster variability, narrower peak in ACF

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PSD ACF

Pow

er d

ensi

ty

Cor

rela

tion

Frequency Time lag