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Title: Interpreting broad emission-line variations - I. Factors influencing the emission-line response
Authors: Goad, Michael R.
Korista, K. T.
First Published: 12-Aug-2014
Publisher: Oxford University Press on behalf of the Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, 2014, 444 (1), pp. 43-61
Abstract: We investigate the sensitivity of the measured broad emission-line responsivity dlog fline/dlog fcont to continuum variations in the context of straw-man broad emission-line region (BLR) geometries of varying size with fixed BLR boundaries, and for which the intrinsic emission-line responsivity is known a priori. We find for a generic emission line that the measured responsivity ηeff, delay and maximum of the cross-correlation function are correlated for characteristic continuum variability time-scales Tchar less than the maximum delay for that line τmax(line) for a particular choice of BLR geometry and observer orientation. The above correlations are manifestations of geometric dilution arising from reverberation effects within the spatially extended BLR. When present, geometric dilution reduces the measured responsivity, delay and maximum of the cross-correlation function. Conversely, geometric dilution is minimized if Tchar ≥ τmax(line). We also find that the measured responsivity and delay show a strong dependence on light-curve duration, with shorter campaigns resulting in smaller than expected values, and only a weak dependence on sampling rate (for irregularly sampled data). The observed strong negative correlation between continuum level and line responsivity found in previous studies cannot be explained by differences in the sampling pattern, light-curve duration or in terms of purely geometrical effects. To explain this and to satisfy the observed positive correlation between continuum luminosity and BLR size in an individual source, the responsivity-weighted radius must increase with increasing continuum luminosity. For a BLR with fixed inner and outer boundaries this requires radial surface emissivity distributions which deviate significantly from a simple power law, and in such a way that the intrinsic emission-line responsivity increases towards larger BLR radii, in line with photoionization calculations.
DOI Link: 10.1093/mnras/stu1456
ISSN: 0035-8711
eISSN: 1365-2966
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2014, The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Deposited with reference to the publisher’s archiving policy available on the SHERPA/RoMEO website.
Description: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2014, The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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