The Sloan Digital Sky Survey Reverberation Mapping Project: UV–Optical Accretion Disk Measurements with the Hubble Space Telescope

Abstract

We present accretion-disk structure measurements from UV–optical reverberation mapping (RM) observations of a sample of eight quasars at 0.24 < z < 0.85. Ultraviolet photometry comes from two cycles of Hubble Space Telescope monitoring, accompanied by multiband optical monitoring by the Las Cumbres Observatory network and Liverpool Telescopes. The targets were selected from the Sloan Digital Sky Survey Reverberation Mapping project sample with reliable black hole mass measurements from Hβ RM results. We measure significant lags between the UV and various optical griz bands using JAVELIN and CREAM methods. We use the significant lag results from both methods to fit the accretion-disk structure using a Markov Chain Monte Carlo approach. We study the accretion disk as a function of disk normalization, temperature scaling, and efficiency. We find direct evidence for diffuse nebular emission from Balmer and Fe ii lines over discrete wavelength ranges. We also find that our best-fit disk color profile is broadly consistent with the Shakura & Sunyaev disk model. We compare our UV–optical lags to the disk sizes inferred from optical–optical lags of the same quasars and find that our results are consistent with these quasars being drawn from a limited high-lag subset of the broader population. Our results are therefore broadly consistent with models that suggest longer disk lags in a subset of quasars, for example, due to a nonzero size of the ionizing corona and/or magnetic heating contributing to the disk response.

Estimating AGN Black Hole Masses via Continuum Reverberation Mapping in the Era of LSST

“…Homayouni et al 2022; G22).A remarkable feature of Figure1is that the two R-L relations are approximately parallel. The Hβ R BLR -L relation has a slope of -+ 0.533 0.033 0.035 , derived byBentz et al (2013) based on a sample of spectroscopically monitored AGNs with luminosity well constrained using Hubble Space Telescope images.…”

“…The R CER was estimated by fitting a power-law function R CER = R CER,0 λ β to the interband (g-r, g-i) lag-wavelength relation. The power-law slope β was fixed to β = 4/3 as suggested by previous AGN CRM studies (Fausnaugh et al 2016;Jiang et al 2017;Homayouni et al 2019;Yu et al 2020;Homayouni et al 2022). The R CER at rest-frame 2500 Å is available in the Table 4 of G22.…”

Negative Lags on the Viscous Timescale in Quasar Photometry and Prospects for Detecting More with LSST

“…Accounting for the five planned 9.6 deg 2 DDF, we can expect to detect around 500 of these quasars within the DDFs. If we take the more conservative fraction of quasars with S/N2 > 20 from Homayouni et al (2022), we find that around 200 quasars should have detectable lags. If we assume only 13% of light curves will have r 0.8 max > as in Guo et al (2022), we would be able to detect long lags for 65 quasars within the DDFs.…”

“…In particular, Blandford & McKee (1982) proposed a technique known as reverberation mapping to measure distances to the BLR, by measuring time lags (of order 100 days) between the continuum emission and broad emission lines (see also Kaspi et al 2000;Peterson et al 2004;Bentz & Katz 2015;Grier et al 2017). A second type of reverberation mapping, first introduced by Collier et al (1999) and known as disk continuum reverberation mapping, uses time lags between variability in different wave bands to measure the radial extent of the disk, using the lamppost model (e.g., Sergeev et al 2005;Cackett et al 2007Cackett et al , 2018De Rosa et al 2015;Edelson et al 2015Edelson et al , 2017Edelson et al , 2019Fausnaugh et al 2016;Jiang et al 2017;Starkey et al 2017;Homayouni et al 2022). The lamppost model proposes that high-frequency (X-ray or hard-UV) emission from the corona will be reprocessed by the disk and reemitted as UV-optical light.…”

Simulating X-Ray Reverberation in the Ultraviolet-emitting Regions of Active Galactic Nuclei Accretion Disks with Three-dimensional Multifrequency Radiation Magnetohydrodynamic Simulations

“…Reverberation mapping was first proposed by Blandford & McKee (1982) as a way to measure distances to the BLR by finding a time lag between variability in continuum light curves and variability in broad emission lines (see also Kaspi et al 2000;Peterson et al 2004;Bentz & Katz 2015;Grier et al 2017). Disk continuum reverberation mapping can similarly be used to measure the radial extent of the accretion disk itself because X-rays emitted by the corona move outwards along the disk and are absorbed and reemitted by different temperature regions of the disk at different wavelengths based on the local temperature (e.g., Sergeev et al 2005;Cackett et al 2007;De Rosa et al 2015;Edelson et al 2015Edelson et al , 2017Edelson et al , 2019Fausnaugh et al 2016;Jiang et al 2017;Starkey et al 2017;Cackett et al 2018Cackett et al , 2021Homayouni et al 2022). Therefore, there will be a lag on the light-crossing timescale between variability in light curves from short wavelength bands and light curves that have been reprocessed and reemitted in longer wavelength bands.…”