Accretion Physics in the SDSS/ XMM-Newton Quasar Survey
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Transcript of Accretion Physics in the SDSS/ XMM-Newton Quasar Survey
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Accretion Physics in the SDSS/XMM-Newton
Quasar Survey
Monica Young
with Martin Elvis, Alan Marscher
& Guido Risaliti
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SDSS/XMM Quasar Survey
• Optical: SDSS DR5 quasars– 90,611 quasars
– 0.1 < z < 5.4
• X-ray: XMM-Newton – Large field of view
• 1% overlap between archive and SDSS
– Large effective area light bucket
• Result: 792 quasars with X-ray observations– Available on HEASARC archive
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3 Optical/X-ray Trends
1. αox-Lopt
2. Γ vs. Lx
3. Γ vs. L/Ledd
X-ray loud
Steffen et al. 2006
X-ray quiet
Shemmer et al. 2008
Green et al. 2009
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3 Optical/X-ray Trends
1. αox-Lopt
2. Γ vs. Lx
3. Γ vs. L/Ledd
X-ray loud
Young et al. 2009
X-ray quiet
Risaliti, Young & Elvis 2009
Young et al. 2009
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Monte Carlo Population Study• Define sample: 106 quasars
– Draw (z,Lopt) randomly from quasar luminosity function (Hopkins et al. 2007)
• Apply SDSS and XMM-Newton selection– SDSS selection/flux limits
– XMM 6σ sensitivity: fn(Texp,θ)
• Find out which relationsare intrinsic to the parent population
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Optical/X-ray Trends
1. The αox-Lopt Relation
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αox = normally distributed around <αox> = -1.6, σ = 0.17
αox = -0.137*log L2500 + 2.64, σ = 0.15 (Steffen+06)
Selection effects cannot reproduce correlation!
Is αox-Lopt Real?
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αox-Lopt stronger effect in X-ray energy
1500 Å 5000 Å
1 keV
4 keV
Slope and scatter change strongly with X-ray energy
log L1500
log L1500
log L5000
log L5000
αo
xα
ox
αo
xα
ox
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Slope of αox-Lopt Relation
• Slope steepest at low X-ray energy
• Closer to linear at highest energies
• Change in correlation slope is not due to change in baseline over which αox is defined
S
lope
of α
ox-L
op
t
X-ray Energy (keV)
“Baseline Effect”
To understand why, need to understand the Γ-Lx anti-corr.
1keV
10keV
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Optical/X-ray Trends
2. The Γ-Lx Relation
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The Γ-Lx Relation
• Significant correlation above 2 keV– Consistent with Green et al. 2009– Strengthens with X-ray energy
2 keV 10 keV
Green+09
Young+09
3.0σ significance 8.6σ significance
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Simulated Γ-Lx Relation: Assume Γ = f(Lbol/LEdd)
log L2 keV
Γ
0.7σ significance 6.0σ significance
log L10 keV
Γ
• Correlation strengthens artificially with energy
• But artificial correlation not significant at L2
Observed slope
Simulated slope
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Simulated Γ-Lx Relation: Assume Γ = f(Lx, Lbol/LEdd)
• If X-ray slope is a function of Lx and Lbol/LEdd, then observed slope, strength reproduced
4.3σ significance 9.0σ significance
Observed slope
Simulated slope
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Γ-Lx Correlation Due to Soft Excess?
• Lx-z correlated (flux-limited) – Soft excess enters X-ray
spectrum at low z
• Make redshift cut: z > 1
Γ-Lx correlation disappears
• Is soft excess strength related to z or to Lx?
– Subject of future study
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Γ-Lx Relation Steepens αox-Lopt
Simulation shows that αox-Lopt slope changes with energy due to Γ-Lx anti-correlationΓ = f(Lbol/Ledd) Γ = f(L2 keV)
ObservedSimulated
X-ray Energy (keV) X-ray Energy (keV)
Slo
pe
of α
ox-L
opt
Slo
pe
of α
ox-L
opt
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αox-Lopt Independent of Baseline
Account for effect of
Γ-Lx relation on αox-Lopt slope
αox-Lopt slope is independent of optical and X-ray reference frequencies
Implies constant αopt, Γ with respect to luminosity
log ν (Hz)
log
νFν (
ergs
cm -
2 s -
1)
Schematic Diagram
X-rays(corona)
Opt/UV (disk)
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What drives αox?
• Lopt is the primary driver of αox
• BUT accretion rate is a secondary driver– Partial correlation (αox, L/LEdd, Lopt) 7σ
X-ray faint
X-ray bright
log L/LEdd
Seed photon luminosity and accretion rate bothdrive X-ray efficiency
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αox and Comptonization Models
• Heating rate ~ lh ~ Lx/Rx
• Cooling rate ~ ls ~ Lo/Ro
• αox lh/ls geometry
lh/ls >> 2 “photon-starved”
lh/ls~2
lhl h
/ls
Coppi 1999
Γ=1.6
T=2e9 K
Thermal Comptonization Model
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Physical Scenario (“Patchy” corona)
As luminosity increases, so does the covering factor (i.e., more blobs).
The corona cools as it intercepts more disk photons.
The optical depth remains constant (τ~0.1), so Γ steepens: ΔΓ~0.2
for ΔL2~1.3 dex.
(comparable to error in Γ)
Low Lbol
High Lbol
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Conclusions• SDSS/XMM-Newton Quasar Survey (SXQS) is a powerful tool!
– 473 quasars with both optical and X-ray spectra – unprecedented sample size!– Monte Carlo population study quantifies selection effects in the survey
• Determine which relations are intrinsic– Γ-Lx – not intrinsic (due to soft excess component at low z)
– αox-Lopt – intrinsic
– αox-Lopt slope constant with respect to the reference frequencies
• Implies αopt and Γ constant with respect to luminosity
• Disk-corona structure changes with L/LEdd
– Use αox-Lopt as input to Comptonization models
– To reproduce αox-Lopt relation, the heating to cooling ratio must decrease
covering factor of corona increases with luminosity (i.e., with L/LEdd?)
• Next step: Defend thesis! (July 15)