A New Class of Changing-Look LINERs

Creators: Frederick, Sara; Gezari, Suvi; Graham, Matthew J.; Cenko, S. Bradley; van Velzen, Sjoert; Stern, Daniel; Blagorodnova, Nadejda; Kulkarni, Shrinivas R.; Yan, Lin; De, Kishalay; Fremling, U. Christoffer; Hung, Tiara; Kara, Erin; Shupe, David L.; Ward, Charlotte; Bellm, Eric C.; Dekany, Richard; Duev, Dmitry A.; Feindt, Ulrich; Giomi, Matteo; Kupfer, Thomas; Laher, Russ R.; Masci, Frank J.; Miller, Adam A.; Ngeow, Chow-Choong; Patterson, Maria T.; Porter, Michael; Rusholme, Ben; Sollerman, Jesper; Walters, Richard; Neill, James D.

Abstract

We report the discovery of six active galactic nuclei (AGNs) caught "turning on" during the first nine months of the Zwicky Transient Facility (ZTF) survey. The host galaxies were classified as low-ionization nuclear emission-line region galaxies (LINERs) by weak narrow forbidden line emission in their archival SDSS spectra, and detected by ZTF as nuclear transients. In five of the cases, we found via follow-up spectroscopy that they had transformed into broad-line AGNs, reminiscent of the changing-look LINER iPTF16bco. In one case, ZTF18aajupnt/AT2018dyk, follow-up Hubble Space Telescope ultraviolet and ground-based optical spectra revealed the transformation into a narrow-line Seyfert 1 with strong [Fe vii, x, xiv] and He ii λ 4686 coronal lines. Swift monitoring observations of this source reveal bright UV emission that tracks the optical flare, accompanied by a luminous soft X-ray flare that peaks ~60 days later. Spitzer follow-up observations also detect a luminous mid-infrared flare, implying a large covering fraction of dust. Archival light curves of the entire sample from CRTS, ATLAS, and ASAS-SN constrain the onset of the optical nuclear flaring from a prolonged quiescent state. Here we present the systematic selection and follow-up of this new class of changing-look LINERs, compare their properties to previously reported changing-look Seyfert galaxies, and conclude that they are a unique class of transients well-suited to test the uncertain physical processes associated with the LINER accretion state.

Additional Information

© 2019 The American Astronomical Society. Received 2019 April 23; revised 2019 August 3; accepted 2019 August 8; published 2019 September 18. We thank the referee for insightful and constructive comments and suggestions. S.G. acknowledges E. Quataert, and S.F. acknowledges R. Mushotzky for useful discussions and J. Ruan for helpful correspondence. We would like to thank S.M. Adams, M. Kuhn, and Y. Sharma for obtaining the Keck and Palomar 200 inch spectral observations. S.G. is supported in part by NSF CAREER grant 1454816, and the XMM-Newton grant for AO-17 Proposal 82204. This work is based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. This work was supported by the GROWTH project funded by the National Science Foundation under grant No. 1545949. These results made use of the Discovery Channel Telescope at Lowell Observatory. Lowell is a private, non-profit institution dedicated to astrophysical research and public appreciation of astronomy and operates the DCT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University and Yale University. The upgrade of the DeVeny optical spectrograph has been funded by a generous grant from John and Ginger Giovale. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work is based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministerio da Ciencia e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina). This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. These observations are associated with program 15331. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Facilities: PO:1.2 m - , PO:1.5 m - , Hale - , DCT - , Keck:I (LRIS) - , Gemini:Gillett - , HST (STIS) - , Swift - , XMM. - Software: HEAsoft (Arnaud 1996), SAS (Gabriel et al. 2004).

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