Probing quasar accretion discs in anomalous lensed quasars Nick Bate David Floyd, Rachel Webster, Stuart Wyithe The University of Melbourne, Australia October 2nd, Oz Lens 2008

1 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

2 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

3 Flux ratio anomalies Multiply imaged quasars with a pair of images straddling a critical curve Simple theoretical arguments suggest we should see magnification ratio A 2 /A 1 ~ 1, equivalently  m ~ 0 (Blandford & Narayan 1986) We don’t! An example: MG –z source = 2.64 –z lens = 0.96 –A 2 /A 1 = 0.45  0.06 (  m A 1 /A 2 = -0.9  0.1) (Schechter & Moore 1993) –  0 = 0.01 parsec cfa- A2A2 A1A1 MG

4 The cause: microlensing Schechter & Wambsganss 2002: images at minima (A 1 ) and saddle points (A 2 ) 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 MinimumSaddle mm mm probability

5 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:

6 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: source size wavelength

7 Observational data Filter r’r’ i’i’ z’z’ JH central (Å) A 2 /A      0.05 FilterF110WF205W central (Å) A 2 /A   0.03 FilterF675WF814W central (Å) A 2 /A   0.01 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-

8 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 A 1 and A 2, for smooth matter 0% -- 99% Microlenses selected from a Salpeter mass function, M max /M min = 50 Microlensing simulations I A 1, 0%A 2, 0% A 1, 90%A 2, 90% Minimum Saddle Point

9 Microlensing simulations II Use Gaussian source brightness profiles, characteristic size  See Mortonson, Schechter and Wambsganss 2005 Create mock A 1 and A 2 observations Divide A 2 magnifications by A 1 magnifications Result: a library of F sim (  ) for each smooth matter percentage

10 Microlensing simulations III Go from F sim (  ) to F sim ( ) using: Thus, we have a library of F sim ( ) for each combination of  0, and smooth matter percentage s compare with F obs ( ), apply Bayes’ Theorem  probability distribution for  0, and s source size wavelength

11 The accretion disc in 0414  0 = 0.01 parsec for MG Shakura-Sunyaev disc (1973): R  (4/3)  0 = 0.01 parsec for MG r’-band size 

12 The accretion disc in 0414 Smooth matter percentage in this lens: unconstrained r’-band emission region size (95%):  0 ≤ 1.80  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 , Poindexter et al 2008 (68%): 1.18 ≤ ≤ 2.16

13 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 (95%): –r’-band emission region ≤ 1.80  cm –0.77 ≤ ≤ 2.67 Bate, Floyd, Webster & Wyithe 2008 (MNRAS, accepted) More systems to follow