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Accretion Physics in the SDSS/ XMM-Newton Quasar Survey

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

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Accretion Physics in the SDSS/ XMM-Newton Quasar Survey

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  1. Accretion Physics in the SDSS/XMM-NewtonQuasar Survey Monica YoungwithMartin Elvis, Alan Marscher& Guido Risaliti

  2. 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. 3 Optical/X-ray Trends X-ray loud 1. αox-Lopt 2. Γ vs. Lx 3.Γ vs. L/Ledd Green et al. 2009 X-ray quiet Steffen et al. 2006 Shemmer et al. 2008

  4. 3 Optical/X-ray Trends X-ray loud 1. αox-Lopt 2. Γ vs. Lx 3.Γ vs. L/Ledd Young et al. 2009 X-ray quiet Young et al. 2009 Risaliti, Young & Elvis 2009

  5. 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

  6. Optical/X-ray Trends 1. The αox-Lopt Relation

  7. Is αox-Lopt Real? 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!

  8. αox-Lopt stronger effect in X-ray energy αox αox 1 keV log L1500 log L5000 1500 Å 5000 Å αox αox 4 keV log L1500 log L5000 Slope and scatter change strongly with X-ray energy

  9. Slope of αox-Lopt Relation Slope of αox-Lopt • 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 “Baseline Effect” 1keV 10keV X-ray Energy (keV) To understand why, need to understand the Γ-Lx anti-corr.

  10. Optical/X-ray Trends 2. The Γ-Lx Relation

  11. The Γ-Lx Relation • Significant correlation above 2 keV • Consistent with Green et al. 2009 • Strengthens with X-ray energy Young+09 Green+09 2 keV 10 keV 3.0σsignificance 8.6σsignificance

  12. Simulated Γ-Lx Relation: Assume Γ= f(Lbol/LEdd) Observed slope Simulated slope • Correlation strengthens artificially with energy • But artificial correlation not significant at L2 Γ Γ log L2 keV log L10 keV 0.7σsignificance 6.0σsignificance

  13. Simulated Γ-Lx Relation: Assume Γ= f(Lx, Lbol/LEdd) Observed slope • If X-ray slope is a function of Lxand Lbol/LEdd, then observed slope, strength reproduced Simulated slope 4.3σsignificance 9.0σsignificance

  14. 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

  15. Γ-Lx Relation Steepens αox-Lopt Simulation shows that αox-Lopt slope changes with energy due to Γ-Lx anti-correlation Γ = f(Lbol/Ledd) Γ = f(L2 keV) Slope of αox-Lopt Slope of αox-Lopt Observed Simulated X-ray Energy (keV) X-ray Energy (keV)

  16. αox-Lopt Independent of Baseline Schematic Diagram 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, Γwith respect to luminosity Opt/UV (disk) log νFν (ergs cm-2 s-1) X-rays (corona) log ν (Hz)

  17. 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 bright  Seed photon luminosity and accretion rate bothdrive X-ray efficiency X-ray faint log L/LEdd

  18. αox and Comptonization Models Thermal Comptonization Model • Heating rate ~ lh ~ Lx/Rx • Cooling rate ~ ls ~ Lo/Ro • αox lh/ls  geometry Γ=1.6 lh/ls T=2e9 K lh/ls~2 lh Coppi 1999 lh/ls >> 2 “photon-starved”

  19. 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 depthremainsconstant (τ~0.1), so Γsteepens: ΔΓ~0.2 • for ΔL2~1.3 dex. • (comparable to error in Γ) Low Lbol High Lbol

  20. 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)

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