Quasar Tomography: Unification of Echo Mapping and Photoionisation Models

Abstract

Reverberation mapping uses time-delayed variations in photoionised emission lines to map the geometry and kinematics of emission-line gas in active galactic nuclei. In previous work, the light travel time delay tau=R(1+cos(theta))/c and Doppler shift v give a 2-d map Psi(tau,v) for each emission line. Here we combine the velocity-delay information with photoionisation physics in a maximum entropy fit to the full reverberating spectrum F_lam(lam,t) to recover a 5-d map of the differential covering fraction f(R,theta,n,N,v), with n and N the density and column density of the gas clouds. We test the method for a variety of geometries (shells, rings, disks, clouds, jets) by recovering a 3-d map f(R,theta,n) from reverberations in 7 uv emission lines. The best test recovers a hollow shell geometry, defining R to 0.15 dex, n to 0.3 dex, and ionisation parameter U ~ 1/(n R^2) to 0.1 dex. The results are sensitive to the adopted distance and luminosity, suggesting that these parameters may be measurable as well.

Accepted 4 Sep 2002 for publication in MNRAS

References in corpus (7)

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• Geometric and Dynamical Models of Reverberation Mapping Data
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• Interpreting broad emission-line variations I : Factors influencing the emission-line response
• Correlations of Quasar Optical Spectra with Radio Morphology
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• High Eddington quasars as discovery tools: current state and challenges
• New Constraints on the Quasar Broad Emission Line Region
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