Journal
NATURE
Volume 573, Issue 7774, Pages 381-+Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41586-019-1556-x
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Funding
- ESA Member States
- Chandra X-ray Observatory
- NASA/ESA Hubble Space Telescope, ATCA
- Karl G. Jansky VLA
- South African MeerKAT radio telescope
- Australian Government
- Spanish public funding [ESP2017-86582-C4-1-R, ESP2015-65597-C4-1-R]
- Spanish State Research Agency (AEI) [ESP2017-87676-C5-1-R, MDM-2017-0737]
- NASA through NASA Hubble Fellowship - Space Telescope Science Institute [HST-HF2-51403.001]
- Oxford Hintze Centre for Astrophysical Surveys from Hintze Family Charitable Foundation
- STFC
- UGC-UKIERI Phase 3 Thematic Partnership
- Fonds de la Recherche Scientifique-FNRS, Belgium [4.4501.19]
- NASA [NAS5-26555]
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In the past two decades, high-amplitude electromagnetic outbursts have been detected from dormant galaxies and often attributed to the tidal disruption of a star by the central black hole(1,2). X-ray emission from the Seyfert 2 galaxy GSN 069 (2MASX J01190869-3411305) at a redshift of z = 0.018 was first detected in July 2010 and implies an X-ray brightening by a factor of more than 240 over ROSAT observations performed 16 years earlier(3,4). The emission has smoothly decayed over time since 2010, possibly indicating a long-lived tidal disruption event(5). The X-ray spectrum is ultra-soft and can be described by accretion disk emission with luminosity proportional to the fourth power of the disk temperature during long-term evolution. Here we report observations of quasi-periodic X-ray eruptions from the nucleus of GSN 069 over the course of 54 days, from December 2018 onwards. During these eruptions, the X-ray count rate increases by up to two orders of magnitude with an event duration of just over an hour and a recurrence time of about nine hours. These eruptions are associated with fast spectral transitions between a cold and a warm phase in the accretion flow around a low-mass black hole (of approximately 4 x 10(5) solar masses) with peak X-ray luminosity of about 5 x 10(42) erg per second. The warm phase has kT (where T is the temperature and k is the Boltzmann constant) of about 120 electronvolts, reminiscent of the typical soft-X-ray excess, an almost universal thermal-like feature in the X-ray spectra of luminous active nuclei(6-8). If the observed properties are not unique to GSN 069, and assuming standard scaling of timescales with black hole mass and accretion properties, typical active galactic nuclei with higher-mass black holes can be expected to exhibit high-amplitude optical to X-ray variability on timescales as short as months or years(9).
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