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 Makishima UT, Shin’ya Yamada UT, Kazuhiro Nakazawa UT, Chris Done (University of Durham)

1. Low/Hard State Pictures Emission mechanism: Thermal Comptonization Geometry: A cool disk and a hot corona Zdziarski 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 High Energy View of Accreting Objects: AGN and X-ray Binaries (Makishima+ 2008) Energy (keV) χ 2 = 1.13 (349) νFν spectrum of Cygnus X-1 νFν spectrum of Cygnus X-1 χ 2 =1.13(349) Hot corona(xspec compPS) –Hard optical depth ~ 1.5 –Soft opt. dep. ~ 0.4 T e ~ 100 keV, R seed ~ 210 km Directly visible cool disk –T in ~ 0.2 keV, R in ~ 250 km Weakly broadened Iron line –E C 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 √R seed 2 + R in 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

5 High Energy View of Accreting Objects: AGN and X-ray Binaries The corona − Seed photons − y-parameter The disk − T in − R in Fe-K line − EW Reflection solid angle − Ω/2π High events Low events From low to high : Intensity Sorted Spectra Disk unchanged!

A cool disk and a hot corona of two optical depth Inner disk radius is ~15 R g (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 diskBH reflection raw disc Compton When XIS count rate is low Corona has many holes

A cool disk and a hot corona of two optical depth Inner disk radius is ~15 R g (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 diskBH reflection raw disc Compton When XIS count rate is high Disk coverage may increase? : 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 (C ASM ) as a soft X-ray flux indicator 8 ● Suzaku Observation 0 60 RXTE ASM ( keV) count rate (s -1 ) 0 2 Hardness (5-12 keV/1.5-3 keV) High Energy View of Accreting Objects: AGN and X-ray Binaries

3-2: Three Representative Spectra: (1) XIS + HXD → Concentrating on hard X-rays High Energy View of Accreting Objects: AGN and X-ray Binaries 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 PINGSO C ASM =14.9 cts/sC ASM =23.3 cts/s C ASM =45.0 cts/s χ 2 /dof =146/134153/135 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 soft X-ray flux photon indexcutoff energy ? The fit was successful on the remaining data sets reflection 140/135 y= 1.39 T e = 76 keV Ω/2π= 0.25 y= 1.26 T e = 85 keV Ω/2π= 0.33 y= 1.00 T e = 78 keV Ω/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

3-5: Reflection vs. ASM count Reflection solid angle increases by ~30% when C ASM triples Gilfanov+ (1999), Zdziarski+ (2000), Ibragimov+ (2005) 12 Ω/2π High Energy View of Accreting Objects: AGN and X-ray Binaries

4-1: Power Spectral Density vs. ASM count When C ASM increases by a factor of 3, time scale of variability ∝ ν b -1 low frequency power decreases by an order of magnitude 13 PIN data (10-60 keV) 50 ms bin s/interval Break frequency (ν b ) Low frequency power (from 0 to 0.01 Hz) High Energy View of Accreting Objects: AGN and X-ray Binaries

4-1: Power Spectral Density vs. ASM count When C ASM increases by a factor of 3, time scale of variability ∝ ν b -1 low frequency power decreases by an order of magnitude 14 PIN data (10-60 keV) 50 ms bin s/interval Break frequency (ν b ) Low frequency power (from 0 to 0.01 Hz) High Energy View of Accreting Objects: AGN and X-ray Binaries νPν

4-2: Energy Dependence of Time Variability 15 Auto correlation of 4 bands Cross correlation with 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 keV one) High Energy View of Accreting Objects: AGN and X-ray Binaries s bin s/interval

5-1: Discussion on Mass Accretion Fluctuation When 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 Disk BH

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 :Discussion on Energy Dependence of Time Variability High Energy View of Accreting Objects: AGN and X-ray Binaries 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 :Discussion on Energy Dependence of Time Variability High Energy View of Accreting Objects: AGN and X-ray Binaries 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 :Discussion on Energy Dependence of Time Variability High Energy View of Accreting Objects: AGN and X-ray Binaries 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

Deeper Analysis of Asymmetry in CCF Parameterize hard lags by taking area ratios (B/A > 1) Hard lags become more significant in softer observations? High 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 component New insight for approaching a corona-disk geometry? High Energy View of Accreting Objects: AGN and X-ray Binaries Corona Disk BH Geometry Energy spectra HXD Harder obs Softer obs High-τ dominant. Less asymmetric Low-τ invades. More asymmetric In the HXD region Low-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 PSDACF Power density Correlation Frequency Time lag