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 redshift z = 0.018 was first detected in 2010 July and implies an X-ray brightening of more than a factor of 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 disc emission with luminosity proportional to the fourth power of the disc temperature during long-term evolution. Here we report observations of X-ray quasi-periodic eruptions from the nucleus of GSN 069 over the course of 54 days, 2018 December onwards. During these eruptions, the X-ray count rate increases by up to two orders of magnitude with event duration of just over 1 hour and recurrence time of about 9 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 Xray luminosity of ~ 5 × 10 42 ergs per second. The warm phase has a temperature 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 6,7,8 . 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 more massive black holes can be expected to exhibit high-amplitude optical to X-ray variability on timescales as short as months or years 9 .Since 2018 December 24, GSN 069 has exhibited peculiar high amplitude, short timescale X-ray variability, first detected during an XMM-Newton observation (XMM3, see Extended Data Table 1).The XMM-Newton light curve is characterized by two bright flares (bursts) with count rate increases by factors of ~ 22 and ~ 31 respectively in the 0.4-2 keV band ( Figure 1a). The bursts are separated by ~ 29.8 ks, their profile is close to symmetric with similar rise and decay times of ~ 1.8 ks, and the total event duration is ~ 4.5 ks. This unexpected X-ray variability prompted us to request a longer XMM-Newton Director Discretionary Time (DDT) observation performed on 2019 January 16/17 (XMM4).Five bursts are detected with varying amplitudes, corresponding to count rate increases by factors of ~ 19 to ~ 28, and longer recurrence time (~ 32.15 ks) than during XMM3 (Figure 1b). Finally, a Chandra DDT observation was performed on 2019 February 14/15 during which three further bursts are detected with count rate variations by factors of ~ 13 to ~ 22, and with recurrence time of ~ 32.7 ks (Figure 1c).We point out that no bursts were observed in a potentially long enough XMM-Newton exposure (83 ks) on 2014 December 5 (XMM2), i.e. 4 years before the X...

We report results from multi-epoch (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013) X-ray observations of the polar-scattered Seyfert 1 galaxy ESO 323-G77. The source exhibits remarkable spectral variability from months to years timescales. The observed spectral variability is entirely due to variations of the column density of a neutral absorber towards the intrinsic nuclear continuum. The column density is generally Compton-thin ranging from a few times 10 22 cm −2 to a few times 10 23 cm −2 . However, one observation reveals a Compton-thick state with column density of the order of 1.5 × 10 24 cm −2 . The observed variability offers a rare opportunity to study the properties of the X-ray absorber(s) in an active galaxy. We identify variable X-ray absorption from two different components, namely (i) a clumpy torus whose individual clumps have a density of 1.7 × 10 8 cm −3 and an average column density of ∼ 4 × 10 22 cm −2 , and (ii) the broad line region (BLR), comprising individual clouds with density of 0.1 − 8 × 10 9 cm −3 and column density of 10 23 − 10 24 cm −2 . The derived properties of the clumpy torus can also be used to estimate the torus half-opening angle, which is of the order of 47 • . We also confirm the previously reported detection of two highly ionized warm absorbers with outflow velocities of 1000 − 4000 km s −1 . The observed outflow velocities are consistent with the Keplerian/escape velocity at the BLR. Hence, the warm absorbers may be tentatively identified with the warm/hot inter-cloud medium which ensures that the BLR clouds are in pressure equilibrium with their surroundings. The BLR line-emitting clouds may well be the cold, dense clumps of this outflow, whose warm/hot phase is likely more homogeneous, as suggested by the lack of strong variability of the warm absorber(s) properties during our monitoring.

We present results obtained from the time-resolved X-ray spectral analysis of the Narrow-Line-Seyfert 1 galaxy SWIFT J2127.4+5654 during a ∼ 130 ks XMM-Newton observation. We reveal large spectral variations, especially during the first ∼ 90 ks of the XMM-Newton exposure. The spectral variability can be attributed to a partial eclipse of the X-ray source by an intervening low-ionization/cold absorbing structure (cloud) with column density N H = 2.0 +0.2 −0.3 ×10 22 cm −2 which gradually covers and then uncovers the X-ray emitting region with covering fraction ranging from zero to ∼ 43 per cent. Our analysis enables us to constrain the size, number density, and location of the absorbing cloud with good accuracy. We infer a cloud size (diameter) of D c 1.5 × 10 13 cm, corresponding to a density of n c 1.5 × 10 9 cm −3 at a distance of R c 4.3 × 10 16 cm from the central black hole. All of the inferred quantities concur to identify the absorbing structure with one single cloud associated with the broad line region of SWIFT J2127.4+5654. We are also able to constrain the X-ray emitting region size (diameter) to be D s 2.3 × 10 13 cm which, assuming the black hole mass estimated from single-epoch optical spectroscopy (1.5 × 10 7 M ⊙ ), translates into D s 10.5 gravitational radii (r g ) with larger sizes (in r g ) being associated with smaller black hole masses, and viceversa. We also confirm the presence of a relativistically distorted reflection component off the inner accretion disc giving rise to a broad relatvistic Fe K emission line and small soft excess (small because of the high Galactic column density), supporting the measurement of an intermediate black hole spin in SWIFT J2127.4+5654 that was obtained from a previous Suzaku observation.

We present a model of the dust environment of Main-Belt Comet P/2010 R2 (La Sagra) from images acquired during the period 2010 October-2011 January. The tails are best simulated by anisotropic ejection models, with emission concentrated near the nucleus south pole, the spin axis having an obliquity near 90 • , indicative of a possible seasonally driven behavior. The dust mass loss rate increases rapidly shortly before perihelion, reaching a maximum value of ∼4 kg s −1 , and maintaining a sustained, cometary-like, activity of about 3-4 kg s −1 up to at least 200 days after perihelion, the date of the latest observation. The size distribution function is characterized by particles in the 5 × 10 −4 cm to 1 cm radius range, assuming a time-constant power-law distribution with an index of −3.5. The ejection velocities are compatible with water-ice sublimation activity at the heliocentric distance of 2.7 AU, with values of 10-20 cm s −1 for particle radius of 1 cm, and inverse square root dependence on particle size, typical of hydrodynamical gas drag.