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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
12.10.10
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
12.10.10
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
12.10.10
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?
12.10.10
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
12.10.10
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
15
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
12.10.10
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.
17
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.
18
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.
19
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.
20 High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10
Deeper Analysis of Asymmetry in CCF
Parameterize hard lags by taking area ratios (B/A > 1)Hard lags become more significant in softer observations?
21 12.10.10High Energy View of Accreting Objects: AGN and X-ray Binaries
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?
22 12.10.10High Energy View of Accreting Objects: AGN and X-ray Binaries
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
23 High Energy View of Accreting Objects: AGN and X-ray Binaries 12.10.10
PSD ACF
Pow
er d
ensi
ty
Cor
rela
tion
Frequency Time lag
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