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Continuum Reverberation Mapping of 18 AGN Over Four Years

Jake A. Miller, Edward M. Cackett, Misty C. Bentz, Michael R. Goad, Kirk T. Korista, Ian M. McHardy

TL;DR

The paper investigates whether optical continuum lags in AGN arise primarily from accretion-disk reprocessing or include significant BLR contributions. It uses four years of high-cadence, multi-band optical photometry from the Zowada Observatory to measure interband lags and infer continuum-emission size scales. The authors find that $\tau_{5100} \propto L_{5100}^{0.4}$, broadly consistent with the theoretical scaling $\tau \propto L^{1/2}$ expected for continuum reverberation from either disk or BLR. These results extend the lag sample and highlight the possible role of BLR diffuse continuum in shaping optical delays, with implications for disk size measurements and AGN structure models.

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 four years of observations to acquire high quality optical continuum light curves, measuring time lags between different photometric bands and determining continuum emission sizes for each AGN. We add this sample to existing lag measurements to test the correlation between continuum lags at $5100Å$ ($τ_{5100}$) and $5100Å$ luminosity ($L_{5100}$). We observe that $τ_{5100} \propto L_{5100}^{0.4}$, broadly consistent with the theoretical expectations of $τ\propto L^{1/2}$ expected for continuum reverberation from either the accretion disk or the BLR.

Continuum Reverberation Mapping of 18 AGN Over Four Years

TL;DR

The paper investigates whether optical continuum lags in AGN arise primarily from accretion-disk reprocessing or include significant BLR contributions. It uses four years of high-cadence, multi-band optical photometry from the Zowada Observatory to measure interband lags and infer continuum-emission size scales. The authors find that , broadly consistent with the theoretical scaling expected for continuum reverberation from either disk or BLR. These results extend the lag sample and highlight the possible role of BLR diffuse continuum in shaping optical delays, with implications for disk size measurements and AGN structure models.

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 four years of observations to acquire high quality optical continuum light curves, measuring time lags between different photometric bands and determining continuum emission sizes for each AGN. We add this sample to existing lag measurements to test the correlation between continuum lags at () and luminosity (). We observe that , broadly consistent with the theoretical expectations of expected for continuum reverberation from either the accretion disk or the BLR.

Paper Structure

This paper contains 2 sections, 1 figure.

Table of Contents

  1. Introduction
  2. Methods

Figures (1)

  • Figure 1: Example $g$-band observation of Mrk 876 taken with Zowada. The red circle indicates the AGN's location, and the magenta circles are the four comparison stars used for the $griz$ relative photometry. The plotted stars had the lowest fractional standard deviation out of 25 stars tested. See Sec. \ref{['sec:methods']} for details.