Accreting supermassive black holes (SMBHs) can exhibit variable emission across the electromagnetic spectrum and over a broad range of timescales. The variability of active galactic nuclei (AGNs) in the ultraviolet and optical is usually at the few tens of per cent level over timescales of hours to weeks1. Recently, rare, more dramatic changes to the emission from accreting SMBHs have been observed, including tidal disruption events2,3,4,5, ‘changing look’ AGNs6,7,8,9 and other extreme variability objects10,11. The physics behind the ‘re-ignition’, enhancement and ‘shut-down’ of accretion onto SMBHs is not entirely understood. Here we present a rapid increase in ultraviolet–optical emission in the centre of a nearby galaxy, marking the onset of sudden increased accretion onto a SMBH. The optical spectrum of this flare, dubbed AT 2017bgt, exhibits a mix of emission features. Some are typical of luminous, unobscured AGNs, but others are likely driven by Bowen fluorescence—robustly linked here with high-velocity gas in the vicinity of the accreting SMBH. The spectral features and increased ultraviolet flux show little evolution over a period of at least 14 months. This disfavours the tidal disruption of a star as their origin, and instead suggests a longer-term event of intensified accretion. Together with two other recently reported events with similar properties, we define a new class of SMBH-related flares. This has important implications for the classification of different types of enhanced accretion onto SMBHs.
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The data that support the findings of this study are available from the corresponding author upon reasonable request. All of our spectra are publicly available on the Weizmann Interactive Supernova data REPository (WISeREP)69. The data used to prepare Supplementary Fig. 1 are available from the ASAS-SN Light Curve Server (https://asas-sn.osu.edu/).
Caplar, N., Lilly, S. J. & Trakhtenbrot, B. Optical variability of AGN in the PTF/iPTF survey. Astrophys. J. 834, 111 (2017).
Gezari, S. et al. An ultraviolet-optical flare from the tidal disruption of a helium-rich stellar core. Nature 485, 217–220 (2012).
Arcavi, I. et al. A continuum of H- to He-rich tidal disruption candidates with a preference for E+A galaxies. Astrophys. J. 793, 38 (2014).
Holoien, T. W. et al. ASASSN-14ae: a tidal disruption event at 200 Mpc. Mon. Not. R. Astron. Soc. 445, 3263–3277 (2014).
Holoien, T. W.-S. et al. Six months of multiwavelength follow-up of the tidal disruption candidate ASASSN-14li and implied TDE rates from ASAS-SN. Mon. Not. R. Astron. Soc. 455, 2918–2935 (2016).
LaMassa, S. M. et al. The discovery of the first ‘changing look’ quasar: new insights into the physics and phenomenology of active galactic nuclei. Astrophys. J. 800, 144 (2015).
MacLeod, C. L. et al. A systematic search for changing-look quasars in SDSS. Mon. Not. R. Astron. Soc. 457, 389–404 (2016).
Ricci, C. et al. IC 751: a new changing look agn discovered by NuSTAR. Astrophys. J. 820, 5 (2016).
Runnoe, J. C. et al. Now you see it, now you don’t: the disappearing central engine of the quasar J1011+5442. Mon. Not. R. Astron. Soc. 455, 1691–1701 (2016).
Lawrence, A. et al. Slow-blue nuclear hypervariables in PanSTARRS-1. Mon. Not. R. Astron. Soc. 463, 296–331 (2016).
Graham, M. J. et al. Understanding extreme quasar optical variability with CRTS I. Major AGN flares. Mon. Not. R. Astron. Soc. 470, 4112–4132 (2017).
Shappee, B. J. et al. The man behind the curtain: X-rays drive the UV through NIR variability in the 2013 active galactic nucleus outburst in NGC 2617. Astrophys. J. 788, 48 (2014).
Kiyota, S. et al. ASASSN-17cu and ASASSN-17cv: discovery of two probable supernovae. Astronomer's Telegram 10113 (2017).
Lusso, E. & Risaliti, G. The tight relation between X-ray and ultraviolet luminosity of quasars. Astrophys. J. 819, 154 (2016).
Vanden Berk, D. E. et al. Composite quasar spectra from the Sloan digital sky survey. Astron. J. 122, 549–564 (2001).
Bennert, N., Falcke, H., Schulz, H., Wilson, A. S. & Wills, B. J. Size and structure of the narrow-line region of quasars. Astrophys. J. 574, L105–L109 (2002).
Mor, R., Netzer, H. & Elitzur, M. Dusty structure around type-I active galactic nuclei: clumpy torus narrow-line region and near-nucleus hot dust. Astrophys. J. 705, 298–313 (2009).
Gezari, S. et al. PS1-10jh continues to follow the fallback accretion rate of a tidally disrupted star. Astrophys. J. 815, L5 (2015).
Brown, J. S. et al. The ultraviolet spectroscopic evolution of the low-luminosity tidal disruption event iPTF16fnl. Mon. Not. R. Astron. Soc. 473, 1130–1144 (2018).
Brown, J. S. et al. The long term evolution of ASASSN-14li. Mon. Not. R. Astron. Soc. 446, 4904–4916 (2017).
Bowen, I. S. The origin of the nebular lines and the structure of the planetary nebulae. Astrophys. J. 67, 1 (1928).
Weymann, R. J. & Williams, R. E. The Bowen fluorescence mechanism in planetary nebulae and the nuclei of Seyfert galaxies. Astrophys. J. 157, 1201 (1969).
Schachter, J., Filippenko, A. V. & Kahn, S. M. Bowen fluorescence in Scorpius X-1. Astrophys. J. 340, 1049 (1989).
Kastner, S. O. & Bhatia, A. K. The Bowen fluorescence lines: overview and re-analysis of the observations. Mon. Not. R. Astron. Soc. 279, 1137–1156 (1996).
Williams, R. E. & Weymann, R. J. Proceedings of the conference on Seyfert galaxies and related objects: 35. Calculated line intensities for models of Seyfert galaxy nuclei. Astron. J. 73, 895 (1968).
Schachter, J., Filippenko, A. V. & Kahn, S. M. Bowen fluorescence in a sample of Seyfert nuclei. Astrophys. J. 362, 74 (1990).
Netzer, H., Elitzur, M. & Ferland, G. J. Bowen fluorescence and He ii lines in active galaxies and gaseous nebulae. Astrophys. J. 299, 752 (1985).
Shemmer, O. et al. Near-Infrared spectroscopy of high-redshift active galactic nuclei. I. A metallicityaccretion rate relationship. Astrophys. J. 614, 547–557 (2004).
Tadhunter, C., Spence, R., Rose, M., Mullaney, J. & Crowther, P. A tidal disruption event in the nearby ultra-luminous infrared galaxy F01004-2237. Nat. Astron. 1, 0061 (2017).
Wyrzykowski, L. et al. OGLE-IV real-time transient search. Acta Astron. 64, 197–232 (2014).
Gromadzki, M., Hamanowicz, A. & Wyrzykowski, L. VLT/FORS2 spectroscopic classification of an unusual nuclear transient OGLE17aaj. Astronomer’s Telegram 9977 (2017).
Wyrzykowski, L. et al. OGLE-IV transient search report 25 September 2017 part 1. Astronomer's Telegram 10776 (2017).
Blanchard, P. K. et al. PS16dtm: a tidal disruption event in a narrow-line Seyfert 1 galaxy. Astrophys. J. 843, 106 (2017).
Kankare, E. et al. A population of highly energetic transient events in the centres of active galaxies. Nat. Astron. 1, 865–871 (2017).
Stanek, K. Z. ASAS-SN transient discovery report for 2017-02-22. Transient Name Server Discovery Report, No. 2017–223 (2017).
Kochanek, C. S. et al. The all-sky automated survey for supernovae (ASAS-SN) light curve server v1.0. Publ. Astron. Soc. Pac. 129, 104502 (2017).
Roming, P. W. A. et al. The Swift ultra-violet/optical telescope. Space Sci. Rev. 120, 95–142 (2005).
Gehrels, N. et al. The Swift gamma ray burst mission. Astrophys. J. 611, 1005–1020 (2004).
Cardelli, J. A., Clayton, G. C. & Mathis, J. S. The relationship between infrared, optical, and ultraviolet extinction. Astrophys. J. 345, 245 (1989).
Wyder, T. K. et al. The ultraviolet galaxy luminosity function in the local universe from GALEX data. Astrophys. J. 619, L15 (2005).
Peng, C. Y., Ho, L. C., Impey, C. D. & Rix, H. Detailed decomposition of galaxy images. II. Beyond axisymmetric models. Astron. J. 139, 2097–2129 (2010).
Tacchella, S. et al. The SINS/zC-SINF survey of z ~ 2 galaxy kinematics: rest-frame morphology, structure, and colors from near-infrared Hubble space telescope imaging. Astrophys. J. 802, 101 (2015).
Voges, W. et al. IAU Circular No. 7432 (ed. Green, D. W. E.) (Central Bureau for Astronomical Telegrams, International Astronomical Union, 2000).
Ranalli, P., Comastri, A. & Setti, G. The 2–10 keV luminosity as a star formation rate indicator. Astron. Astrophys. 399, 39–50 (2003).
Helfand, D. J., White, R. L. & Becker, R. H. The last of FIRST: the final catalog and source identifications. Astrophys. J. 801, 26 (2015).
Yun, M. S., Reddy, N. A. & Condon, J. Radio properties of infraredselected galaxies in the IRAS 2 Jy sample. Astrophys. J. 554, 803–822 (2001).
Hopkins, A. M. et al. Star formation rate indicators in the Sloan digital sky survey. Astrophys. J. 599, 971–991 (2003).
Heckman, T. M. & Best, P. N. The coevolution of galaxies and supermassive black holes: insights from surveys of the contemporary universe. Annu. Rev. Astron. Astrophys. 52, 589–660 (2014).
Padovani, P. The faint radio sky: radio astronomy becomes mainstream. Astron. Astrophys. Rev. 24, 1–61 (2016).
Kennicutt, R. C. Star formation in galaxies along the Hubble sequence. Annu. Rev. Astron. Astrophys. 36, 189–231 (1998).
Salim, S. et al. UV star formation rates in the local universe. Astrophys. J. Suppl. 173, 267–292 (2007).
Just, D. W. et al. The X-ray properties of the most luminous quasars from the Sloan digital sky survey. Astrophys. J. 665, 1004–1022 (2007).
Bruzual, G. & Charlot, S. Stellar population synthesis at the resolution of 2003. Mon. Not. R. Astron. Soc. 344, 1000 (2003).
Wright, E. L. et al. The Wide-field Infrared Survey Explorer (WISE): mission description and initial on-orbit performance. Astron. J. 140, 1868–1881 (2010).
Stern, D. et al. Mid-infrared selection of active galactic nuclei with the Wide-field Infrared Survey Explorer. I. Characterizing WISE-selected active galactic nuclei in COSMOS. Astrophys. J. 753, 30 (2012).
Burrows, D. N. et al. The Swift X-ray telescope. Space Sci. Rev. 120, 165–195 (2005).
Trakhtenbrot, B. et al. BAT AGN spectroscopic survey (BASS) VI. The ΓXL/LEdd relation. Mon. Not. R. Astron. Soc. 470, 800–814 (2017).
Fabian, A. C. et al. Long XMM observation of the narrow-line Seyfert 1 galaxy IRAS 13224-3809: rapid variability, high spin and a soft lag. Mon. Not. R. Astron. Soc. 429, 2917–2923 (2013).
Fabian, A. C. et al. Broad line emission from iron K- and L-shell transitions in the active galaxy 1H 0707-495. Nature 459, 540–542 (2009).
Ricci, C. et al. Suzaku observation of IRAS 00521-7054, a peculiar type-II AGN with a very broad feature at 6 keV. Astrophys. J. 795, 147 (2014).
Harrison, F. A. et al. The Nuclear Spectroscopic Telescope Array (NuSTAR) high-energy X-ray mission. Astrophys. J. 770, 103 (2013).
Madsen, K. K. et al. Calibration of the NuSTAR high-energy focusing X-ray telescope. Astrophys. J. Suppl. 220, 8 (2015).
Gendreau, K. C., Arzoumanian, Z. & Okajima, T. The Neutron star Interior Composition ExploreR (NICER): an explorer mission of opportunity for soft X-ray timing spectroscopy. Proc. SPIE 8443, 844313 (2012).
Gierliński, M. & Done, C. Is the soft excess in active galactic nuclei real? Mon. Not. R. Astron. Soc. 349, L7–L11 (2004).
Crummy, J., Fabian, A. C., Gallo, L. & Ross, R. R. An explanation for the soft X-ray excess in active galactic nuclei. Mon. Not. R. Astron. Soc. 365, 1067–1081 (2005).
Winter, L. M., Veilleux, S., McKernan, B. & Kallman, T. R. The Swift burst alert telescope detected Seyfert 1 galaxies: X-ray broadband properties and warm absorbers. Astrophys. J. 745, 107 (2012).
Ricci, C. et al. BAT AGN spectroscopic survey—V. X-ray properties of the Swift/BAT 70-month AGN catalog. Astrophys. J. Suppl. 233, 17 (2017).
Brown, T. M. et al. Las Cumbres observatory global telescope network. Publ. Astron. Soc. Pac. 125, 1031–1055 (2013).
Yaron, O. & Gal-Yam, A. WISeREP—an interactive supernova data repository. Publ. Astron. Soc. Pac. 124, 668–681 (2012).
Trakhtenbrot, B. & Netzer, H. Black hole growth to z = 2—I. Improved virial methods for measuring M BH and L/L Edd. Mon. Not. R. Astron. Soc. 427, 3081–3102 (2012).
Kewley, L. J., Heisler, C. A., Dopita, M. A. & Lumsden, S. Optical classification of southern warm infrared galaxies. Astrophys. J. Suppl. 132, 37–71 (2001).
Kauffmann, G. et al. The host galaxies of active galactic nuclei. Mon. Not. R. Astron. Soc. 346, 1055–1077 (2003).
Schawinski, K. et al. Observational evidence for AGN feedback in early-type galaxies. Mon. Not. R. Astron. Soc. 382, 1415–1431 (2007).
Baldwin, J. A., Phillips, M. M. & Terlevich, R. Classification parameters for the emissionline spectra of extragalactic objects. Publ. Astron. Soc. Pac. 93, 5 (1981).
Peterson, B. M. et al. The size of the narrow-line-emitting region in the Seyfer 1 galaxy NGC 5548 from emission-line variability. Astrophys. J. 779, 109 (2013).
Simcoe, R. A. et al. FIRE: a near-infrared cross-dispersed echellette spectrometer for the Magellan telescopes. Proc. SPIE 7014, 70140U (2008).
Eikenberry, S. S. et al. FLAMINGOS-2: the facility near-infrared wide-field imager and multi-object spectrograph for Gemini. Proc. SPIE 5492, 1196–1207 (2004).
Glikman, E., Helfand, D. J. & White, R. L. A near-infrared spectral template for quasars. Astrophys. J. 640, 579–591 (2006).
Marconi, A. et al. Local supermassive black holes, relics of active galactic nuclei and the X-ray background. Mon. Not. R. Astron. Soc. 351, 169–185 (2004).
Runnoe, J. C., Brotherton, M. S. & Shang, Z. Updating quasar bolometric luminosity corrections. Mon. Not. R. Astron. Soc. 422, 478–493 (2012).
Netzer, H. et al. Star formation black hole growth and dusty tori in the most luminous AGNs at z = 2–3.5. Astrophys. J. 819, 123 (2016).
Kaspi, S. et al. Reverberation measurements for 17 quasars and the size-mass-luminosity relations in active galactic nuclei. Astrophys. J. 533, 631–649 (2000).
Shen, Y. The mass of quasars. Bull. Astron. Soc. Ind. 41, 61–115 (2013).
Peterson, B. M. Measuring the masses of supermassive black holes. Space Sci. Rev. 183, 253–275 (2014).
Mejía-Restrepo, J. E., Trakhtenbrot, B., Lira, P., Netzer, H. & Capellupo, D. M. Active galactic nuclei at z ~ 1.5 II. Black hole mass estimation by means of broad emission lines. Mon. Not. R. Astron. Soc. 460, 187–211 (2016).
Bentz, M. C. et al. The low-luminosity end of the radius-luminosity relationship for active galactic nuclei. Astrophys. J. 767, 149 (2013).
Kaspi, S. et al. The relationship between luminosity and broad-line region size in active galactic nuclei. Astrophys. J. 629, 61–71 (2005).
Pei, L. et al. Space telescope and optical reverberation mapping project. V. Optical spectroscopic campaign and emission-line analysis for NGC 5548. Astrophys. J. 837, 131 (2017).
Holoien, T. W.-S. et al. ASASSN-15oi: a rapidly evolving, luminous tidal disruption event at 216 Mpc. Mon. Not. R. Astron. Soc. 463, 3813–3828 (2016).
Blagorodnova, N. et al. iPTF16fnl: a faint and fast tidal disruption event in an E+A galaxy. Astrophys. J. 844, 46 (2017).
Hung, T. et al. Revisiting optical tidal disruption events with iPTF16axa. Astrophys. J. 842, 29 (2017).
MacLeod, M., Guillochon, J. & Ramirez-Ruiz, E. The tidal disruption of giant stars and their contribution to the flaring supermassive black hole population. Astrophys. J. 757, 134 (2012).
Lin, D. et al. A luminous X-ray outburst from an intermediate-mass black hole in an offcentre star cluster. Nat. Astron. 2, 656–661 (2018).
Mattila, S. et al. A dust-enshrouded tidal disruption event with a resolved radio jet in a galaxy merger. Science 361, 482–485 (2018).
Moriya, T. J., Tanaka, M., Morokuma, T. & Ohsuga, K. Superluminous transients at AGN centers from interaction between black hole disk winds and broad-line region clouds. Astrophys. J. 843, L19 (2017).
Netzer, H. & Marziani, P. The effect of radiation pressure on emission-line profiles and black holes mass determination in active galactic nuclei. Astrophys. J. 724, 318–328 (2010).
Campana, S. et al. Multiple tidal disruption flares in the active galaxy IC 3599. Astron. Astrophys. 581, A17 (2015).
Grupe, D., Komossa, S. & Saxton, R. IC 3599 did it again: a second outburst of the X-ray transient Seyfert 1.9 galaxy. Astrophys. J. 803, L28 (2015).
Metzger, B. D. & Stone, N. C. Periodic accretion-powered flares from colliding EMRIs as TDE imposters. Astrophys. J. 844, 75 (2017).
Farris, B. D., Duffell, P., MacFadyen, A. I. & Haiman, Z. Characteristic signatures in the thermal emission from accreting binary black holes. Mon. Not. R. Astron. Soc. 446, L36–L40 (2015).
Frank, J., King, A. & Raine, D. J. Accretion Power in Astrophysics 3rd edn (Cambridge Univ. Press, Cambridge, 2002).
Netzer, H. The Physics and Evolution of Active Galactic Nuclei (Cambridge Univ. Press, Cambridge, 2013).
Stern, D. et al. A mid-IR selected changing-look quasar and physical scenarios for abrupt AGN fading. Astrophys. J. 864, 27 (2018).
B.T. is a Zwicky Fellow. I.A. is an Einstein Fellow. E.K. is a Hubble Fellow. We thank N. Caplar, J. Guillochon, Z. Haiman, E. Lusso, and K. Schawinski for useful discussions. We thank C. Tadhunter for providing the spectrum of the F01004-2237 transient and his helpful comments. Part of this work was inspired by discussions within International Team #371, ‘Using Tidal Disruption Events to Study Super-Massive Black Holes’, hosted at the International Space Science Institute in Bern, Switzerland. We thank all the participants of the team meeting for their beneficial comments. Support for I.A. was provided by NASA through the Einstein Fellowship Program, grant PF6-170148. C.R. acknowledges support from the CONICYT + PAI Convocatoria Nacional subvencion a instalacion en la academia convocatoria a no 2017 PAI77170080. P.G.J. acknowledges support from European Research Council Consolidator Grant 647208. A. Horesh acknowledges support by the I-Core Program of the Planning and Budgeting Committee and the Israel Science Foundation. G.H., D.A.H. and C.M. acknowledge support from NSF grant AST-1313484. M.B. acknowledges support from the Black Hole Initiative at Harvard University, which is funded by a grant from the John Templeton Foundation. G.L. acknowledges support from a Herchel Smith Research Fellowship of the University of Cambridge. Ł.W., M.G. and A. Hamanowicz acknowledge Polish National Science Centre grant OPUS no 2015/17/B/ST9/03167 to Ł.W. Research by D.J.S. is supported by NSF grants AST-1412504 and AST-1517649. E.Y.H. acknowledges the support provided by the National Science Foundation under Grant No. AST-1613472 and by the Florida Space Grant Consortium. This work makes use of observations from the Las Cumbres Observatory network. This publication also makes use of data products from the Wide-field Infrared Survey Explorer. WISE and NEOWISE are funded by the National Aeronautics and Space Administration.
This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR operations, software and calibration teams for support with the execution and analysis of these observations. This research made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).
We thank the Swift, NuSTAR and NICER teams for scheduling and performing the target-of-opportunity observations presented here on short notice. The LRIS spectrum presented herein was obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation. We recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
These results made use of the Discovery Channel Telescope (DCT) 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 FLAMINGOS-2 spectrum was obtained at the Gemini Observatory under program GS-2017A-Q-33 (PI: Sand), which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership: the National Science Foundation (USA), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina) and Ministério da Ciência, Tecnologia e Inovação (Brazil).
The authors declare no competing interests.
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Trakhtenbrot, B., Arcavi, I., Ricci, C. et al. A new class of flares from accreting supermassive black holes. Nat Astron 3, 242–250 (2019). https://doi.org/10.1038/s41550-018-0661-3