Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 ≡ the Einstein Cross. II. Energy profile of the accretion disk
Abstract
We present the continuation of our long-term spectroscopic monitoring of the gravitationally lensed quasar QSO 2237+0305. We investigate the chromatic variations observed in the UV/optical continuum of both quasar images A and B, and compare them with numerical simulations to infer the energy profile of the quasar accretion disk. Our procedure combines the microlensing ray-shooting technique with Bayesian analysis, and derives probability distributions for the source sizes as a function of wavelength. We find that the effective caustic crossing timescale is 4.0 ± 1.0 months. Using a robust prior on the effective transverse velocity, we find that the source responsible for the UV/optical continuum has an energy profile well reproduced by a power-law R ∝ λζ with ζ=1.2 ± 0.3, where R is the source size responsible for the emission at wavelength λ. This is the first accurate, model-independent determination of the energy profile of a quasar accretion disk on such small scales.
Based on observations made with ESO Telescopes at the Paranal Observatory under program ID 073.B-0243, 074.B-0270, 075.B-0350, 076.B-0197, 177.B-0615.- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 2008
- DOI:
- 10.1051/0004-6361:200810729
- arXiv:
- arXiv:0810.0011
- Bibcode:
- 2008A&A...490..933E
- Keywords:
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- gravitational lensing;
- quasars: individual: QSO 2237+0305;
- accretion;
- accretion disks;
- Astrophysics
- E-Print:
- 13 pages, 5 figures, minor corrections, matching final version published in A&