Accretion Physics in the SDSS/XMM-Newton

Quasar Survey

Monica Young

with Martin Elvis, Alan Marscher

& Guido Risaliti

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

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

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

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

Optical/X-ray Trends

1. The αox-Lopt Relation

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?

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

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

Optical/X-ray Trends

2. The Γ-Lx Relation

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

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

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

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

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

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)

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

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

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

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)