The Astrophysical Journal (Jan 2023)

AGN STORM 2. IV. Swift X-Ray and Ultraviolet/Optical Monitoring of Mrk 817

  • Edward M. Cackett,
  • Jonathan Gelbord,
  • Aaron J. Barth,
  • Gisella De Rosa,
  • Rick Edelson,
  • Michael R. Goad,
  • Yasaman Homayouni,
  • Keith Horne,
  • Erin A. Kara,
  • Gerard A. Kriss,
  • Kirk T. Korista,
  • Hermine Landt,
  • Rachel Plesha,
  • Nahum Arav,
  • Misty C. Bentz,
  • Benjamin D. Boizelle,
  • Elena Dalla Bontà,
  • Maryam Dehghanian,
  • Fergus Donnan,
  • Pu Du,
  • Gary J. Ferland,
  • Carina Fian,
  • Alexei V. Filippenko,
  • Diego H. González Buitrago,
  • Catherine J. Grier,
  • Patrick B. Hall,
  • Chen Hu,
  • Dragana Ilić,
  • Jelle Kaastra,
  • Shai Kaspi,
  • Christopher S. Kochanek,
  • Andjelka B. Kovačević,
  • Daniel Kynoch,
  • Yan-Rong Li,
  • Jacob N. McLane,
  • Missagh Mehdipour,
  • Jake A. Miller,
  • John Montano,
  • Hagai Netzer,
  • Christos Panagiotou,
  • Ethan Partington,
  • Luka Č. Popović,
  • Daniel Proga,
  • Daniele Rogantini,
  • David Sanmartim,
  • Matthew R. Siebert,
  • Thaisa Storchi-Bergmann,
  • Marianne Vestergaard,
  • Jian-Min Wang,
  • Tim Waters,
  • Fatima Zaidouni

DOI
https://doi.org/10.3847/1538-4357/acfdac
Journal volume & issue
Vol. 958, no. 2
p. 195

Abstract

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The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels. The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble Space Telescope UV continuum light curves, we measure interband continuum lags, τ ( λ ), that increase with increasing wavelength roughly following τ ( λ ) ∝ λ ^4/3 , the dependence expected for a geometrically thin, optically thick, centrally illuminated disk. Modeling of the light curves reveals a period at the beginning of the campaign where the response of the continuum is suppressed compared to later in the light curve—the light curves are not simple shifted and scaled versions of each other. The interval of suppressed response corresponds to a period of high UV line and X-ray absorption, and reduced emission line variability amplitudes. We suggest that this indicates a significant contribution to the continuum from the broad-line region gas that sees an absorbed ionizing continuum.

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