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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
are needed to see this picture.
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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
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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