Changing look: from Compton‐thick to Compton‐thin, or the rebirth of fossil active galactic nuclei

By G. Matt, M. Guainazzi, R. Maiolino. 2003

194 citations recorded by the source corpus.

We discuss the properties of a small sample of type 2 Seyfert galaxies whose X-ray spectra changed appearance on time-scales of years, becoming reflection-dominated from Compton-thin, or vice versa. A reflection-dominated spectrum is usually taken as evidence of Compton-thick absorption, but we instead argue that such a spectrum is due to a temporary switching-off of the nuclear radiation. The observations discussed here may help to explain mismatches between optical and X-ray classifications, and provide new strong and direct evidence for the presence of more than one cold circumnuclear region in type 2 Seyfert galaxies.

Subfields: Astronomy and Astrophysics, Radiation

View Paper: https://www.semanticscholar.org/paper/ca043411f705f754c586762ad0bab59da85e4bd1

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Citations in the corpus

Discovery of 21 New Changing-look AGNs in the Northern Sky (2017, methodology): “The term “changing-look” was originally used in X-ray, in which objects were found to change from Comptonthick to Compton-thin, or vice versa (e.g., Matt et al. 2003; Bianchi et al. 2005; Ballo et al. 2008; Piconcelli et al. 2007; Risaliti et al. 2009; Marchese et al. 2012; Ricci et al. 2016).”
X-ray obscuration and obscured AGN in the local universe (2005, background): “In a few bright, nearby Seyfert 2s, for which high resolution spectroscopic measurements have been possible (Sako et al. 2000, Sambruna et al. 2001, Kinkhabwala et al. 2002), soft X-rays are dominated by emission lines from highly ionized species due mainly to recombination and resonant scattering f”
Rapid Compton-thick/Compton-thin Transitions in the Seyfert 2 Galaxy NGC 1365 (2005, background): “Similar switching from reflection-dominated to transmissiondominated states has now been observed in a handful sources on timescales of a few years (Matt et al. 2003) and could be due either to extreme variations of the intrinsic luminosity, and therefore of the ionization state of the absorber (as…”
THE DISCOVERY OF THE FIRST “CHANGING LOOK” QUASAR: NEW INSIGHTS INTO THE PHYSICS AND PHENOMENOLOGY OF ACTIVE GALACTIC NUCLEI (2014, background): “Variable X-ray absorption has been observed in what have been dubbed “changing-look” AGN (e.g., Matt et al. 2003; Puccetti et al. 2007; Bianchi et al. 2009; Risaliti et al. 2009; Marchese et al. 2012); these variations result from gas clouds moving into and out of the line-of-sight.”
THE MAN BEHIND THE CURTAIN: X-RAYS DRIVE THE UV THROUGH NIR VARIABILITY IN THE 2013 ACTIVE GALACTIC NUCLEUS OUTBURST IN NGC 2617 (2013, background): ““Changing-look”AGN have been observed in X-rays as well (e.g., Matt et al. 2003).”
Resolving the mid-infrared cores of local Seyferts (2009, background): “NGC 6300 This is one of a sample of ‘changing-look’ AGN whose spectra exhibit transitions between Compton-thick and Compton-thi obscuration on timescales of years (Matt et al. 2003).”
Active galactic nuclei: what’s in a name? (2017, background): “…have shown that the X-ray and optical spectral properties of AGN can vary on relatively short timescales as a result of changes in the absorbing column density along the line of sight (e.g. Risaliti et al. 2002, 2005; Matt et al. 2003; MacLeod et al. 2016; Ruan et al. 2016; see also Sect.”
Now You See It, Now You Don't: The Disappearing Central Engine of the Quasar J1011+5442 (2015, methodology): “The term “changing-look” was initially used to describe Xray AGN with variable obscuration (e.g., Matt et al. 2003; Puccetti et al. 2007; Bianchi et al. 2009; Risaliti et al. 2009; Marchese et al. 2012), but has lately widened to include objects that transition between Types 1 and 2 (an optical…”