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Echo mapping of active galactic nuclei broad-line regions: Fundamental algorithmsWe formulate and test a series of algorithms for echo mapping the emission-line regions near active galactic nuclei from measurements of correlated variability in their line and continuum light curves. The linear regularization method (LRM) employs a direct inversion of evenly spaced light-curve data, with a regularization parameter that can be used to control the trade-off between noise and resolution. Matrix formulas express the formal solution as well as its variance and covariance in terms of uncertainties in the measurements. Unlike the maximum-entropy method (MEM), LRM applies to kernels with both positive and negative values, but the results are somewhat limited by ringing effects. A positivity constraint proves effective in controlling the ringing. MEM combines regularization and positivity in a natural way, but similar results are also found using positivity constraints with nonentropic regularization functions. Direct inversions of unevenly sampled light curves require interpolating the noisy data. In this case better results are found by solving for both the continuum light curve and kernel function in a simultaneous fit to the data. Our conclusion is that while echo mapping currently gives ambiguous results, the algorithms are not the limiting factor. Progress depends on efforts to increase the accuracy and completeness of sampling of the observed light curves.
Document ID
19950050111
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Vio, Roberto
(ESA IUE Observatory Madrid, Spain)
Horne, Keith
(University of Utrecht Utrecht, Netherlands)
Wamsteker, Willem
(ESA IUE Observatory Madrid, Spain)
Date Acquired
August 16, 2013
Publication Date
October 1, 1994
Publication Information
Publication: Astronomical Society of the Pacific, Publications
Volume: 106
Issue: 704
ISSN: 0004-6280
Subject Category
Astrophysics
Accession Number
95A81710
Funding Number(s)
CONTRACT_GRANT: NAGW-2678
Distribution Limits
Public
Copyright
Other

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