Lag‐Luminosity Relationship for Interband Lags between Variations inB,V,R, andIBands in Active Galactic Nuclei

Abstract

We determine interband lags between variations in the B band and variations in the V, R, and I bands for 14 active galactic nuclei observed at the Crimean Astrophysical Observatory. The computed lags range from tenths of a day to several days, and it is positive (that is, V, R, and I bands lag behind the B band) in most cases, except for a few cases for the V filter. In some cases, the lag is greater than zero, with more than 3 confidence. The lag is systematically less for the V filter than for the red filters, and the lag determined from the cross-correlation function (CCF) centroid is systematically greater than the lag determined from the CCF peak. We find that the lag scales with luminosity as L b , where b % 0:4-0.5. We attribute this lag to the light time travel effect, so it reflects the geometrical size of the region that emits optical continuum. We consider a model in which optical emission is mainly reprocessed emission that arises in the accretion disk heated by an X-ray source above the disk.

The Structure of the Broad-line Region in Active Galactic Nuclei. II. Dynamical Modeling of Data From the AGN10 Reverberation Mapping Campaign

“…It is possible that our assumption of continuum emission originating at r = 0 could cause us to underestimate M BH , although it is also worth noting that NGC 5548 was in an exceptional state during the course of this RM campaign and the emission-line time delays were all shorter than predicted from the radius-luminosity relation (Pei et al 2017). Time delays between the EUV and optical of varying quality and significance have been reported by several other studies as well (Collier et al 1998;Sergeev et al 2005;McHardy et al 2014;Shappee et al 2014;Edelson et al 2015), suggesting that the situation is not unique.…”

Space Telescope and Optical Reverberation Mapping Project. V. Optical Spectroscopic Campaign and Emission-line Analysis for NGC 5548

“…However, wavelengths shorter than ∼3200Å are inaccessible from the ground, so the rest-frame optical continuum is often used as a proxy for the ionizing source in low-redshift AGNs. Although the far-UV and optical continua have been shown to vary almost simultaneously in some cases (e.g., Clavel et al 1991;Reichert et al 1994;Korista et al 1995;Wanders et al 1997), more recent high-cadence studies have found that the optical continuum can lag the UV continuum by up to a few days (Collier et al 1998;Sergeev et al 2005;McHardy et al 2014;Shappee et al 2014;Edelson et al 2015;Fausnaugh et al 2016). This can significantly affect the measured broadline lag if the BLR has a characteristic radius on the order of light-days.…”

The Quasar Accretion Disk Size-Black Hole Mass Relation

“…Quasar accretion disks cannot be spatially resolved with ordinary telescopes, so we have been forced to test accretion physics through time variability (e.g., Vanden Berk et al 2004;Sergeev et al 2005;Cackett et al 2007) and spectral modeling (e.g., Sun & Malkan 1989;Collin et al 2002;Bonning et al 2007). One notable success is the use of reverberation mapping (e.g., Peterson et al 2004) of quasar broad-line emission to calibrate the relation between emission line widths and black hole masses.…”

“…One notable success is the use of reverberation mapping (e.g., Peterson et al 2004) of quasar broad-line emission to calibrate the relation between emission line widths and black hole masses. The line emission, though, comes from scales much larger than the accretion disk, and attempts to use similar methods on the continuum emission have had limited success, largely because quasars show little optical variability on the disk light-crossing timescale (Collin et al 2002;Sergeev et al 2005).…”