Probing quasar accretion discs in anomalous

lensed quasarsNick Bate

David Floyd, Rachel Webster, Stuart Wyithe

The University of Melbourne, AustraliaOctober 2nd, Oz Lens 2008

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Motivation

• Quasar accretion disc models poorly constrained by observations– (Blaes 2007 review)

• Why? Accretion discs are very small!

• Direct imaging not currently possible

Gravitational telescopes!

Lewis 1995

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Standard microlensing analyses

• Aim to constrain the size of quasar emission regions

• Require monitoring campaigns– (eg: Kochanek 2004; Morgan et al

2007, 2008; Anguita et al 2008; Poindexter et al 2008)

• But: – Expensive in terms of telescope

time– Degeneracy between size and

velocity

• Alternative: lensed quasars displaying a flux ratio anomaly

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Flux ratio anomalies• Multiply imaged quasars with a pair

of images straddling a critical curve

• Simple theoretical arguments suggest we should see magnification ratio A2/A1 ~ 1, equivalently m ~ 0 (Blandford & Narayan 1986)

• We don’t!• An example: MG 0414+0534

– zsource = 2.64– zlens = 0.96– A2/A1 = 0.45 0.06

(mA1/A2 = -0.9 0.1)(Schechter & Moore 1993)

0 = 0.01 parsec cfa-www.harvard.edu/castles

A2

A1

MG 0414+0534

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The cause: microlensing

• Schechter & Wambsganss 2002: images at minima (A1) and saddle points (A2) in the time delay surface behave differently when microlensed by a combination of smooth and clumpy matter

• See also: Congdon, Keeton & Osmer 2007; Bate, Wyithe & Webster 2008

Minimum Saddle

m m

pro

bab

ility

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How do we use this information?

• Probability of observing a flux ratio anomaly depends on source size and smooth matter content of the lens

• Conduct microlensing simulations for a range of source sizes () and smooth matter percentages (s)

• Invert using Bayes’ Theorem:QuickTime™ and a decompressor

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Probing accretion discs

• Accretion disc models: longer wavelengths are emitted at larger radii

• Multi-band observations size constraints for multiple emission regions in the source

• We can fit a power-law: QuickTime™ and a

decompressorare needed to see this picture.

source size

wavelength

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QuickTime™ and a decompressor

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Observational data

Filter r’ i’ z’ J H

central (Å) 6231 7625 9134 12500 16500

A2/A1 0.210.1 0.260.1 0.340.10.60.

20.670.0

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Filter F110W F205W

central (Å) 11250 20650

A2/A10.640.0

40.830.03

Filter F675W F814W

central (Å) 6714 7940

A2/A10.400.0

10.470.01

Magellan 6.5-m Baade Telescope, 2007 November 3

IMACS and PANIC

HST, 1997 August 14

NICMOS

HST, 1994 November 8

WFPC2

CASTLES Survey: cfa-www.harvard.edu/castles

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• Use an inverse ray-shooting technique (Kayser, Refsdal & Stabell 1986; Wambsganss, Paczynski & Katz 1990)

• Lens model from Witt, Mao & Schechter 1995

• Generate magnification maps for images A1 and A2, for smooth matter 0% -- 99%

• Microlenses selected from a Salpeter mass function, Mmax/Mmin = 50

Microlensing simulations I

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A1, 0%

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A2, 0%

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A1, 90%

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A2, 90%

Minimum

Saddle Point

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Microlensing simulations II

• Use Gaussian source brightness profiles, characteristic size

• See Mortonson, Schechter and Wambsganss 2005

• Create mock A1 and A2 observations

• Divide A2 magnifications by A1 magnifications

• Result: a library of 25500 Fsim() for each smooth matter percentage

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Microlensing simulations III

• Go from Fsim() to Fsim() using:

• Thus, we have a library of 25500 Fsim() for each combination of 0, and smooth matter percentage s

• compare with Fobs(), apply Bayes’ Theorem probability distribution for 0, and s

QuickTime™ and a decompressor

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source size

wavelength

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QuickTime™ and a decompressor

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The accretion disc in 0414

0 = 0.01 parsec for MG 0414+0534• Shakura-Sunyaev disc (1973): R (4/3)

0 = 0.01 parsec for MG 0414+0534

r’-band

size

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The accretion disc in 0414

• Smooth matter percentage in this lens:unconstrained

• r’-band emission region size (95%):

0 ≤ 1.80 1016 h-1/2 (M/M)1/2 cm

• power-law index (95%):0.77 ≤ ≤ 2.67

• power-law index (68%): 1.05 ≤ ≤ 2.08

• HE 1104-1805, Poindexter et al 2008 (68%):1.18 ≤ ≤ 2.16

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Conclusions

• Demonstrated a method for probing quasar accretion discs with multi-band imaging– No need for monitoring cheap!– Independent of unknown source transverse velocity

• The accretion disc in MG 0414+0534 (95%):– r’-band emission region ≤ 1.80 1016 cm– 0.77 ≤ ≤ 2.67

• Bate, Floyd, Webster & Wyithe 2008 (MNRAS, accepted)

• More systems to follow