Changing-look Event in NGC 3516: Continuum or Obscuration Variability?

The Seyfert-1 galaxy NGC 3516 has undergone major spectral changes in recent years. In 2017 we obtained Chandra, NuSTAR, and Swift observations during its new low-flux state. Using these observations, we model the spectral energy distribution (SED) and the intrinsic X-ray absorption, and compare the...

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Bibliographic Details
Published in:The Astrophysical journal 2022-01, Vol.925 (1), p.84
Main Authors: Mehdipour, Missagh, Kriss, Gerard A., Brenneman, Laura W., Costantini, Elisa, Kaastra, Jelle S., Branduardi-Raymont, Graziella, Di Gesu, Laura, Ebrero, Jacobo, Mao, Junjie
Format: Article
Language:English
Subjects:
Absorbers
Absorption
Accretion disks
Active galactic nuclei
Astrophysics
Emission
Emission lines
Fluctuations
Galaxies
High energy astrophysics
Ionization
Luminosity
Occultation
Outflow
Radiation
Seyfert galaxies
Spectral energy distribution
Spectroscopy
Variability
X ray absorption
X ray sources
X ray spectra
X-ray active galactic nuclei
X-ray emissions
X-ray observatories
X-rays
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Summary:The Seyfert-1 galaxy NGC 3516 has undergone major spectral changes in recent years. In 2017 we obtained Chandra, NuSTAR, and Swift observations during its new low-flux state. Using these observations, we model the spectral energy distribution (SED) and the intrinsic X-ray absorption, and compare the results with those from historical observations taken in 2006. We thereby investigate the effects of the changing-look phenomenon on the accretion-powered radiation and the ionized outflows. Compared to its normal high-flux state in 2006, the intrinsic bolometric luminosity of NGC 3516 was lower by a factor of 4–8 during 2017. Our SED modeling shows a significant decline in the luminosity of all the continuum components from the accretion disk and the X-ray source. As a consequence, the reprocessed X-ray emission lines have also become fainter. The Swift monitoring of NGC 3516 shows remarkable X-ray spectral variability on short (weeks) and long (years) timescales. We investigate whether this variability is driven by obscuration or the intrinsic continuum. We find that the new low-flux spectrum of NGC 3516, and its variability, do not require any new or variable obscuration, and instead can be explained by changes in the ionizing SED that result in the lowering of the ionization of the warm-absorber outflows. This in turn induces enhanced X-ray absorption by the warm-absorber outflows, mimicking the presence of new obscuring gas. Using the response of the ionized regions to the SED changes, we place constraints on their densities and locations.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ac42ca