Abstract

The local (z = 0.0315) active galactic nucleus (AGN) Mrk 817 was monitored over more than 500 days with space- borne and ground-based instruments as part of a large international campaign, AGN STORM 2. Here, we present a comprehensive analysis of the broadband continuum variations using detailed modeling of the broad line region (BLR), several types of disk winds classified by their optical depth, and new numerical simulations. We find that diffuse continuum (DC) emission, with additional contributions from strong and broad emission lines, can explain the continuum lags observed in this source during high- and low-luminosity phases. Disk illumination by the variable X-ray corona contributes only a small fraction of the observed continuum lags. Our BLR models assume radiation-pressure-confined clouds distributed over a distance of 2–122 light days. We present calculated mean emissivity radii of many emission lines, and DC emission, and suggest a simple, transfer-function-dependent method that ties them to cross-correlation lag determinations. We do not find clear indications for large-optical- depth winds, but identify the signature of lower-column-density winds. In particular, we associate the shortest observed continuum lags with a combination of τ(1 Ryd) ≈ 2 wind and a partly shielded BLR. Even smaller optical depth winds may be associated with X-ray absorption features and with noticeable variations in the widths and lags of several high-ionization lines like He II and C IV . Finally, we demonstrate the effect of torus dust emission on the observed lags in the i and z bands.

Document Type

Article

Publication Date

2024

Notes/Citation Information

© 2024. The Author(s). Published by the American Astronomical Society

Digital Object Identifier (DOI)

https://doi.org/10.3847/1538-4357/ad8160

Funding Information

This article is part of the series of papers by the AGN STORM 2 collaboration. Our project began with the successful Cycle 28 HST proposal 16196 (B. M. Peterson et al. 2020). Support for Hubble Space Telescope program GO-16196 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We are grateful to the dedicated Institute staff who worked hard to review and implement this program. We particularly thank the Program Coordinator, W. Januszewski, who made sure the intensive monitoring schedule and coordination with other facilities continued successfully. D.I., A.B.K, and L.Č.P. acknowledge funding provided by the University of Belgrade Faculty of Mathematics (contract 451-03-66/2024-03/200104) and Astronomical Observatory Belgrade (contract 451-03-66/2024-03/200002), through grants by the Ministry of Education, Science, and Technological Development of the Republic of Serbia. D.I. acknowledges the support of the Alexander von Humboldt Foundation. A.B.K. and L.Č.P. are grateful for the support from the Chinese Academy of Science's Presidentʼs International Fellowship Initiative (PIFI) for visiting scientists. N.A. acknowledges support from NSF grant AST 2106249 and NASA STScI grants AR-15786, AR-16600, AR-16601, and HST-AR-17556. G.K. and G.D.R acknowledge support from STScI grant GO- 16196. We thank Jonathan Stern for useful discussions about RPC models. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) license to the Author Accepted Manuscript version arising from this submission.

Download

Share

COinS