Nine-hour X-ray quasi-periodic eruptions from a low-mass black hole galactic nucleus

• Published in: Nature (London) 2019-09, Vol.573 (7774), p.381-384
• Main Authors: Miniutti, G., Saxton, R. D., Giustini, M., Alexander, K. D., Fender, R. P., Heywood, I., Monageng, I., Coriat, M., Tzioumis, A. K., Read, A. M., Knigge, C., Gandhi, P., Pretorius, M. L., Agís-González, B.
• Format: Article
• Language: English
• Subjects: 639/33/34/4118; 639/33/34/4121; 639/33/34/4122; 639/33/34/863; 639/33/34/864; Accretion disks; Active galactic nuclei; Amplitudes; Analysis; Astrophysics; Black holes; Black holes (Astronomy); Brightening; Disruption; Emission; Emissions; Energy; Eruptions; Galaxies; Humanities and Social Sciences; Letter; Luminosity; multidisciplinary; Nuclei; Observations; Outbursts; Physics; Red shift; Science; Science (multidisciplinary); Seyfert galaxies; X ray spectra; X-ray emissions; X-rays
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-019-1556-x

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 × 10 5  solar masses) with peak X-ray luminosity of about 5 × 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 . Galaxy GSN 069 has unprecedented eruptions of X-ray light every nine hours, which indicate fast transitions between cold and warm states and may shed light on black hole accretion.