Changing-look Event in NGC 3516: Continuum or Obscuration Variability?
The Astrophysical Journal, vol. 925, pp. 84
Abstract
Abstract 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.
Authors 9
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Missagh Mehdipour corresponding
Space Telescope Science Institute
Affiliation as printed
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA; mmehdipour@stsci.edu
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
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Space Telescope Science Institute
Affiliation as printed
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA; mmehdipour@stsci.edu
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
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Center for Astrophysics Harvard & Smithsonian
Affiliation as printed
Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
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Space Research Organisation Netherlands · University of Amsterdam
Affiliation as printed
Anton Pannekoek Institute, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
SRON Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
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Leiden University · Leiden Observatory · Space Research Organisation Netherlands
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
SRON Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
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Affiliation as printed
Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
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Laura Di Gesu corresponding
Affiliation as printed
Italian Space Agency (ASI), Via del Politecnico snc, I-00133, Roma, Italy
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European Space Agency · European Space Astronomy Centre
Affiliation as printed
Telespazio UK for the European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo,s/n, E-28692 Villanueva de la Cañada, Madrid, Spain
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Hiroshima University · University of Strathclyde · Space Research Organisation Netherlands
Affiliation as printed
Department of Physics, Hiroshima University, 1-3-1 Kagamiyama, Higashihiroshima, Hiroshima 739-8526, Japan
Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK
SRON Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
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