Transfer function analysis of ultraviolet observations of NGC 5548.

Abstract

A general linear transfer function relating an input series (UV continuum flux) to an output series (emission-line flux) is presented. The methodology for fitting the transfer function is briefly described. The autocorrelation structure of IUE observations of NGC 5548 in different spectral bands is investigated, and appropriate univariate autoregressive moving average models given. The results of extensive transfer function fitting, using respectively the λλ1337 and 1350 continuum variations as input series, are presented. There is little evidence for a dead time in the response of the emission-line variations, which are presumed to be driven by the continuum.