Insight Into "Changing-Look" AGN Mrk 1018 from the Fe K$\alpha$ Line: The Reprocessing Gas Has Yet to Fully Respond to the Fading of the AGN

Abstract

Mrk 1018 is a "changing-look" AGN whose optical spectrum transitioned from a Type 1.9 to Type 1 between 1979 and 1984 and back to a Type 1.9 in 2015. This latest transition was accompanied by a decrease in X-ray flux. We analyze the Chandra spectra from 2010 and 2016 and NuSTAR spectra from 2016, carefully treating pile-up in the Chandra spectrum from 2010 and self-consistently modeling absorption, reflection, and Fe K$\alpha$ line emission in the X-ray spectra from 2016. We demonstrate that while the 2-10 keV X-ray flux decreased by an order of magnitude (1.46${}_{-0.13}^{+0.10}\times 10^{-11}$ erg s${}^{-1}$ cm${}^{-2}$ to 1.31${}_{-0.04}^{+0.09}\times 10^{-12}$ erg s${}^{-1}$ cm${}^{-2}$), the Fe K$\alpha$ equivalent width (EW) increased from 0.18${}_{-0.12}^{+0.17}$ to 0.61${}_{-0.25}^{+0.27}$ keV, due to a depressed AGN continuum. We jointly fit the Chandra and NuSTAR spectra from 2016 using the physically-motivated MYTorus model, finding that the torus orientation is consistent with a face-on geometry, and lines of sight intersecting the torus are ruled out. While we measure no line-of-sight absorption, we measure a column density of $N_{\mathrm{H}}$ = 5.38${}_{-4.0}^{+14}\times 10^{22}$ cm${}^{-2}$ for gas out of the line-of-sight which reprocesses the X-ray emission. We find a high relative normalization between the Compton scattered emission and transmitted continuum, indicative of time lags between the primary X-ray source and reprocessing gas. We predict that the Fe K$\alpha$ line will respond to the decrease in AGN flux, which would manifest as a decrease in the Fe K$\alpha$ EW.

6 pages emulateapj style, 4 Figures, 2 Tables; accepted for publication in ApJ

References in corpus (10)

• The Discovery of the First "Changing Look" Quasar: New Insights into the Physics & Phenomenology of AGN
• On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies
• A Systematic Search for Changing-Look Quasars in SDSS
• AGN Type-casting: Mrk 590 No Longer Fits the Role
• Towards an Understanding of Changing-Look Quasars: An Archival Spectroscopic Search in SDSS
• The Close AGN Reference Survey (CARS) - Mrk 1018 returns to the shadows after 30 years as a Seyfert 1
• The XMM-Newton long look of NGC 1365: uncovering of the obscured X-ray source
• IC 751: a new changing-look AGN discovered by NuSTAR
• The Close AGN Reference Survey (CARS) - What is causing Mrk1018's return to the shadows after 30 years?
• Delving Into X-ray Obscuration of Type 2 AGN, Near and Far

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