Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published September 20, 2019 | Published + Submitted
Journal Article Open

1ES 1927+654: an AGN Caught Changing Look on a Timescale of Months


We study the sudden optical and ultraviolet (UV) brightening of 1ES 1927+654, which until now was known as a narrow-line active galactic nucleus (AGN). 1ES 1927+654 was part of the small and peculiar class of "true Type-2" AGNs that lack broad emission lines and line-of-sight obscuration. Our high-cadence spectroscopic monitoring captures the appearance of a blue, featureless continuum, followed several weeks later by the appearance of broad Balmer emission lines. This timescale is generally consistent with the expected light travel time between the central engine and the broadline emission region in (persistent) broadline AGN. Hubble Space Telescope spectroscopy reveals no evidence for broad UV emission lines (e.g., C iv λ1549, C iii] λ1909, Mg ii λ2798), probably owing to dust in the broadline emission region. To the best of our knowledge, this is the first case where the lag between the change in continuum and in broadline emission of a "changing look" AGN has been temporally resolved. The nature and timescales of the photometric and spectral evolution disfavor both a change in line-of-sight obscuration and a change of the overall rate of gas inflow as driving the drastic spectral transformations seen in this AGN. Although the peak luminosity and timescales are consistent with those of tidal disruption events seen in inactive galaxies, the spectral properties are not. The X-ray emission displays a markedly different behavior, with frequent flares on timescales of hours to days, and will be presented in a companion publication.

Additional Information

© 2019 The American Astronomical Society. Received 2019 March 25; revised 2019 June 25; accepted 2019 July 13; published 2019 September 24. We are grateful to the anonymous referee for helping us improve this manuscript. We thank Gwen Eadie, Bryce Bolin, and Dino Bektešević at UW for assistance with obtaining the APO spectra. We also thank Hagai Netzer, Dalya Baron, and Robert Antonucci for their insightful and constructive comments. R.L. was supported by the National Key R&D Program of China (2016YFA0400702) and the National Science Foundation of China (11721303). I.A. acknowledges support from the Israel Science Foundation (grant No. 2108/18). Support for J.L.P. is provided in part by FONDECYT through the grant 1191038 and by the Ministry of Economy, Development, and Tourisms Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. Support for A.V.F.'s research group has been provided by the TABASGO Foundation, the Christopher R. Redlich Fund, and the Miller Institute for Basic Research in Science (U.C. Berkeley). This work made use of the MATLAB package for astronomy and astrophysics (Ofek 2014) and Astropy,30 a community-developed core Python package for Astronomy (The Astropy Collaboration et al. 2013, 2018). This research also 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. This work made use of data from Las Cumbres Observatory; the All Sky Automated Survey for Supernovae (ASAS-SN); the Asteroid Terrestrial-impact Last Alert System (ATLAS) project; the Liverpool Telescope; the Lick Observatory; and the W. M. Keck Observatory. ATLAS is primarily funded to search for near earth asteroids (NEOs) through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, the Space Telescope Science Institute, and the South African Astronomical Observatory. ASAS-SN is supported by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University and NSF grant AST-1515927. Development of ASAS-SN has been supported by NSF grant AST-0908816, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics at the Ohio State University (CCAPP), the Chinese Academy of Sciences South America Center for Astronomy (CASSACA), the Villum Foundation, and George Skestos. We thank the Las Cumbres Observatory and its staff for its continuing support of the ASAS-SN project. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, with financial support from the UK Science and Technology Facilities Council. Research at Lick Observatory is partially supported by a generous gift from Google. 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. We finally thank NASA HEASARC for making the Swift and NICER data available, and ESA for providing the XMM-Newton data. Facilities: HST (STIS) - , HST (COS) - , Swift (XRT and UVOT) - , NICER - , XMM - , ATLAS - , ASAS-SN - , MDM Observatory (OSMOS) - , Liverpool Telescope (SPRAT) - , Lick Observatory (Shane/Kast) - , Las Cumbres Observatory (FLOYDS) - , Keck (LRIS). - Software: astropy (The Astropy Collaboration et al. 2013, 2018), SExtractor (Bertin & Arnouts 1996), MAAT (Ofek 2014).

Attached Files

Published - Trakhtenbrot_2019_ApJ_883_94.pdf

Submitted - 1903.11084.pdf


Files (3.0 MB)
Name Size Download all
1.1 MB Preview Download
1.8 MB Preview Download

Additional details

August 19, 2023
October 20, 2023