Space Telescope and Optical Reverberation Mapping Project. VIII. Time Variability of Emission and Absorption in NGC 5548 Based on Modeling the Ultraviolet Spectrum

Abstract

We model the ultraviolet spectra of the Seyfert 1 galaxy NGC 5548 obtained with the Hubble Space Telescope during the 6 month reverberation mapping campaign in 2014. Our model of the emission from NGC 5548 corrects for overlying absorption and deblends the individual emission lines. Using the modeled spectra, we measure the response to continuum variations for the deblended and absorption-corrected individual broad emission lines, the velocity-dependent profiles of Lyα and C iv, and the narrow and broad intrinsic absorption features. We find that the time lags for the corrected emission lines are comparable to those for the original data. The velocity-binned lag profiles of Lyα and C iv have a double-peaked structure indicative of a truncated Keplerian disk. The narrow absorption lines show a delayed response to continuum variations corresponding to recombination in gas with a density of ∼105 cm−3. The high-ionization narrow absorption lines decorrelate from continuum variations during the same period as the broad emission lines. Analyzing the response of these absorption lines during this period shows that the ionizing flux is diminished in strength relative to the far-ultraviolet continuum. The broad absorption lines associated with the X-ray obscurer decrease in strength during this same time interval. The appearance of X-ray obscuration in ∼2012 corresponds with an increase in the luminosity of NGC 5548 following an extended low state. We suggest that the obscurer is a disk wind triggered by the brightening of NGC 5548 following the decrease in size of the broad-line region during the preceding low-luminosity state.

Corona-heated Accretion-disk Reprocessing: A Physical Model to Decipher the Melody of AGN UV/Optical Twinkling

“…That is, the probability that the required α for Zw 229-15 is smaller than that for kplr12158940 is less than 10% × 10% = 1%. uum is preferentially suppressed due to, e.g., the intrinsic change of the corona/disk structure (Mathur et al 2017;Sun et al 2018b) or external variations in line-of-sight obscuration (Dehghanian et al 2019;Kriss et al 2019). Indeed, if we split the full multi-wavelength light curves of NGC 5548 into two segments at HJD − 2450000 < 6747, the first portions are more variable than the second ones, especially on timescales longer than 10 days (see Figure 5 of Sun et al 2018b).…”

Testing broad-line region models with reverberation mapping

“…The most detailed studies, so far, involve the intermediate luminosity AGN NGC 5548. This object was the target of three very large optical- UV campaigns, in 1989UV campaigns, in , 1993UV campaigns, in and 2014, and a large number of additional spaceborne and ground-based campaigns (see Pei et al 2017;Korista & Goad 2019;Kriss et al 2019, and references therein). Except for several years of very low luminosity, which will not be discussed here, the SED is dominated by a strong X-ray continuum which is substantially different from the three other SEDs studied in this work.…”

“…The RPC clouds model presented here were applied to the luminosity and SED of NGC 5548 during 2014. I used the line and continuum observations described in Lawther et al (2018), Pei et al (2017) and Kriss et al (2019) and assumed the SED properties detailed in §3.1. Using the Bentz et al (2013) normalization, R Hβ ≈ 16 ld, about twice the lag measured during the STORM 2014 campaign and close to the 25-year mean for this source (Pei et al 2017).…”

“…⋆ E-mail: hagainetzer@gmail.com Progress in reverberation mapping (RM) of the BLR gas provides an opportunity to map the location and motion of the gas, and to estimate the BH mass (MBH). RM measurements are now available for a large number of broad emission lines: Hα, Hβ, Lyα, C iv1549, He ii 1640, He ii 4686, Mg ii 2798, and several blends of Fe ii lines (Kaspi et al 2000;Bentz et al 2010Bentz et al , 2013Hu et al 2015;Du et al 2015;Grier et al 2017;Pei et al 2017;Lira et al 2018;Kriss et al 2019). They have been used to derive the "mean emissivity radius" (RME) and the "mean responsivity radius" of many lines, and to demonstrate that these radii increase roughly in proportion to L5100 1/2 , where L5100 is the monochromatic continuum luminosity at 5100Å in erg s −1 .…”

“…,Netzer et al (1995),Kaspi et al (2000),Telfer et al (2002),Kim, Im & Kim (2010),Bentz et al (2010),Bentz et al (2013),Lira et al (2018),Pei et al (2017) andKriss et al (2019). The line luminosities are normalized to L(Hβ), and the line lags to R Hβ /c.…”