Steps toward Determination of the Size and Structure of the Broad‐Line Region in Active Galactic Nuclei. XVI. A 13 Year Study of Spectral Variability in NGC 5548

Abstract

We present the final installment of an intensive 13-year study of variations of the optical continuum and broad Hβ emission line in the Seyfert 1 galaxy NGC 5548. The data base consists of 1530 optical continuum measurements and 1248 Hβ measurements. The Hβ variations follow the continuum variations closely, with a typical time delay of about 20 days. However, a year-by-year analysis shows that the magnitude of emission-line time delay is correlated with the mean continuum flux. We argue that the data are consistent with the simple model prediction between the size of the broad-line region and the ionizing luminosity, r ∝ L 1/2 ion . Moreover, the apparently linear nature of the correlation between the Hβ response time and the nonstellar optical continuum F opt arises as a consequence of the changing shape of the continuum as it varies, specifically F opt ∝ F 0.56 UV .

Spectroscopic Indication of a Centi-Parsec Supermassive Black Hole Binary in the Galactic Center of Ngc 5548

“…NGC5548 has been observed many times individually (e.g., Iijima & Rafanelli 1995;Shapovalova et al 2004;Sergeev et al 2007;Popović et al 2008), and 16 monitoring campaigns have been devoted to reverberation mapping of the Hβ emission line (e.g., Peterson et al 2002;Bentz et al 2007Bentz et al , 2009Denney et al 2010). In Tables 1 and 2, we compile spectroscopic and photometric data available in the literature and list the corresponding references.…”

“…The majority of the spectroscopic data comes from Sergeev et al (2007, S07;see (Peterson et al 2002). Sergeev et al measured the 5100 Å continuum and decomposed the broad Hβ profiles with the narrow-line component subtracted, and kindly made them available to us.…”

“…It turns out that only the data from source SDSS06 and from this work require a correction. Note that the AGN Watch project 8 published their full data for 5100 Å continuum and integrated Hβ fluxes in Peterson et al (2002), and Sergeev et al (2007) included only the highquality spectra of the AGN Watch project in their compilation. Therefore, these two data sources partially overlap.…”

“…As one of the best-observed nearby AGNs, the Seyfert1 galaxy NGC5548 (z = 0.017175) has been intensively monitored on short and long timescales, especially at optical/UV wavelengths (e.g., Iijima & Rafanelli 1995;Peterson et al 2002;Sergeev et al 2007;Popović et al 2008;Bentz et al 2009; Denney et al 2010;De Rosa et al 2015;Fausnaugh et al 2016). The earliest available data for the optical continuum date back to 1968 , and for Hβ back to 1972 (Sergeev et al 2007), spanning a time range of over four decades.…”

AGN Reverberation Mapping

“…But the general behavior that we observe is the same: in a single AGN, if the central luminosity increases, then the time delay we measure for any specific emission line becomes larger (e.g., Peterson et al 2002;Bentz et al 2007;Kilerci Eser et al 2015). It is important to keep in mind that we are not measuring a geometrical radius, such as an inner or outer boundary of the BLR, with emission-line reverberation mapping.…”