Continuum Reverberation Mapping of 18 Active Galactic Nuclei over 4 Yr

Abstract Continuum reverberation mapping probes the size scale of the optical continuum-emitting region in active galactic nuclei (AGN). The source of this emission has long been thought to originate from the accretion disk, but recent studies suggest the broad-line region (BLR) may significantly contribute to both the observed flux and continuum interband delays. We monitored 18 AGN over 4 yr of observations to acquire high-quality optical continuum light curves, measuring time lags between different photometric bands and determining continuum emission sizes for each active galactic nucleus. We add this sample to existing lag measurements to test the correlation between continuum lags at 5100 Å ( τ 5100 ) and 5100 Å luminosity ( L 5100 ). We observe that <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>τ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>5100</mml:mn> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>5100</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>0.4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , broadly consistent with the theoretical expectations of τ ∝ L 1/2 expected for continuum reverberation from either the accretion disk or the BLR.