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

LaMassa, Stephanie M. and Yaqoob, Tahir and Kilgard, Roy (2017) Insight Into "Changing-Look" AGN Mrk 1018 from the Fe Kα Line: The Reprocessing Gas Has Yet to Fully Respond to the Fading of the AGN. Astrophysical Journal, 840 (1). Art. No. 11. ISSN 1538-4357. doi:10.3847/1538-4357/aa68df.

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Mrk 1018 is a "changing-look" active galactic nucleus (AGN) whose optical spectrum transitioned from a Type 1.9 to a Type 1 between 1979 and 1984, and then 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, with a careful treatment of pileup in the Chandraspectrum from 2010, and self-consistently model absorption, reflection, and Fe Kα 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^(+0.10)_(-0.13) x 10^(-11) -1.31^(+0.09)_(-0.04) erg s^(−1) cm^(−2)), the Fe Kα equivalent width (EW) increased from 0.18^(+0.17)_(-0.12) to 0.61^(+0.27)_(-0.25) keV due to a depressed AGN continuum. We jointly fit the Chandraand NuSTAR spectra from 2016 using the physically motivated MYTorus model, and find that the torus orientation is consistent with a face-on geometry and that lines of sight intersecting the torus are ruled out. While we measure no line-of-sight absorption, we do measure a column density of N_H = 5.38^(+14)_(-4.0) x 10^(22) cm^(−2) for gas out of the line of sight that reprocesses the X-ray emission. We find a high relative normalization between the Compton-scattered emission and transmitted continuum, which is indicative of time lags between the primary X-ray source and reprocessing gas. We predict that the Fe Kα line will respond to the decrease in AGN flux, which would manifest as a decrease in the Fe Kα EW.

Item Type:Article
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URLURL TypeDescription Paper
LaMassa, Stephanie M.0000-0002-5907-3330
Additional Information:© 2017 The American Astronomical Society. Received 2017 March 6; revised 2017 March 19; accepted 2017 March 21; published 2017 April 27. We thank the anonymous referee for a careful reading of this manuscript. S.M.L. is grateful for helpful conversations with J.R.R. Rigby when preparing this manuscript. The scientific results reported in this article are based to a significant degree on observations made by the Chandra X-ray Observatory. This research has made use of software provided by the Chandra X-ray Center (CXC) in the application packages CIAO, ChIPS, and Sherpa. Facilities: CXO - Chandra X-ray Observatory satellite, NuSTAR.
Subject Keywords:galaxies: Seyfert – X-rays: individual (Mrk 1018)
Issue or Number:1
Record Number:CaltechAUTHORS:20170327-090132926
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Official Citation:Stephanie M. LaMassa et al 2017 ApJ 840 11
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75406
Deposited By: Joy Painter
Deposited On:27 Mar 2017 16:07
Last Modified:15 Nov 2021 16:33

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