AGN STORM 2. XI. Spectroscopic Reverberation Mapping of the Hot Dust in Mrk 817

Authors

• Hermine Landt, Durham UniversityFollow
• Benjamin D. Boizelle, Brigham Young University
• Michael S. Brotherton, University of Wyoming
• Laura Ferrarese, National Research Council of Canada
• Travis Fischer, Space Telescope Science Institute
• Varoujan Gorjian, Jet Propulsion Laboratory, California Institute of Technology
• Michael D. Joner, Brigham Young University
• Daniel Kynoch, University of Southampton
• Jacob N. McLane, University of Wyoming
• Jake A.J. Mitchell, Durham University
• John W. Montano, University of California Irvine
• Rogemar A. Riffel, Universidade Federal de Santa Maria
• David Sanmartim, Rubin Observatory Project Office
• Thaisa Storchi-Bergmann, Universidad Federal do Rio Grande do Sul (UFRGS)
• Martin J. Ward, Durham University
• Aaron J. Barth, University of California Irvine
• Edward M. Cackett, Wayne State University
• Gisella De Rosa, Space Telescope Science Institute
• Rick Edelson, Eureka Scientific Inc.
• Jonathan Gelbord, Spectral Sciences Inc.
• Yasaman Homayouni, Space Telescope Science Institute
• Keith Horne, University of St Andrews
• Erin A. Kara, MIT Kavli Institute for Astrophysics and Space Research
• Gerard A. Kriss, Space Telescope Science Institute
• Nahum Arav, Virginia Polytechnic Institute and State University
• Elena Dalla Bontà, University of Padova
• Maryam Dehghanian, University of KentuckyFollow
• Gary J. Ferland, University of KentuckyFollow
• Carina Fian, University of Valencia
• Diego H. González Buitrago, Universidad Nacional Autónoma de México
• Dragana Ilić, University of Belgrade
• Shai Kaspi, Tel Aviv University

Abstract

The AGN Space Telescope and Optical Reverberation Mapping (STORM) 2 campaign targeted Mrk 817 with intensive multiwavelength monitoring and found its soft X-ray emission to be strongly absorbed. We present results from 157 near-IR spectra with an average cadence of a few days. Whereas the hot dust reverberation signal as tracked by the continuum flux does not have a clear response, we recover a dust reverberation radius of ∼90 lt-days from the blackbody dust temperature light curve. This radius is consistent with previous photometric reverberation mapping results when Mrk 817 was in an unobscured state. The heating/cooling process we observe indicates that the inner limit of the dusty torus is set by a process other than sublimation, rendering it a luminosity-invariant “dusty wall” of a carbonaceous composition. Assuming thermal equilibrium for dust optically thick to the incident radiation, we derive a luminosity of ∼6 × 10⁴⁴ erg s⁻¹ for the source heating it. This luminosity is similar to that of the obscured spectral energy distribution, assuming a disk with an Eddington accretion rate of m ̇ ∼ 0.2 . Alternatively, the dust is illuminated by an unobscured lower luminosity disk with m ̇ ∼ 0.1 , which permits the UV-optical continuum lags in the high-obscuration state to be dominated by diffuse emission from the broad-line region. Finally, we find hot dust extended on scales ≳ 140-350 pc, associated with the rotating disk of ionised gas we observe in spatially resolved [S III] λ9531 images. Its likely origin is in the compact bulge of the barred spiral host galaxy, where it is heated by a nuclear starburst.

Document Type

Article

Publication Date

1-20-2026

Notes/Citation Information

Publisher Copyright: © 2026. The Author(s). Published by the American Astronomical Society.

Digital Object Identifier (DOI)

10.3847/1538-4357/ae17cd

Archival?

Archival

Repository Citation

Landt, Hermine; Boizelle, Benjamin D.; Brotherton, Michael S.; Ferrarese, Laura; Fischer, Travis; Gorjian, Varoujan; Joner, Michael D.; Kynoch, Daniel; McLane, Jacob N.; Mitchell, Jake A.J.; Montano, John W.; Riffel, Rogemar A.; Sanmartim, David; Storchi-Bergmann, Thaisa; Ward, Martin J.; Barth, Aaron J.; Cackett, Edward M.; De Rosa, Gisella; Edelson, Rick; Gelbord, Jonathan; Homayouni, Yasaman; Horne, Keith; Kara, Erin A.; Kriss, Gerard A.; Arav, Nahum; Dalla Bontà, Elena; Dehghanian, Maryam; Ferland, Gary J.; Fian, Carina; González Buitrago, Diego H.; Ilić, Dragana; and Kaspi, Shai, "AGN STORM 2. XI. Spectroscopic Reverberation Mapping of the Hot Dust in Mrk 817" (2026). Physics and Astronomy Faculty Publications. 790.
https://uknowledge.uky.edu/physastron_facpub/790