Tidal disruption of stars by supermassive black holes: The X-ray view

Abstract

Abstract. The tidal disruption of stars by supermassive black holes produces luminous soft X-ray accretion flares in otherwise inactive galaxies. First events have been discovered in X-rays with the ROSAT observatory, and have more recently been detected with XMM-Newton, Chandra and Swift, and at other wavelengths. In X-rays, they typically appear as very soft, exceptionally luminous outbursts of radiation, which decline consistent with L ∝ t −5/3 on the timescale of months to years. They reach total amplitudes of decline up to factors 1000-6000 more than a decade after their initial high-states, and in low-state, their host galaxies are essentially X-ray inactive, optically inactive, and radio inactive. X-ray luminous tidal disruption events (TDEs) represent a powerful new probe of accretion physics near the event horizon, and of relativistic effects. TDEs offer a new way of estimating black hole spin, and they are signposts of supermassive binary black holes and recoiling black holes. Once discovered in the thousands in upcoming sky surveys, their rates will probe stellar dynamics in distant galaxies, and they will uncover theso far elusive -population of intermediate mass black holes in the universe, if they do exist. Further, the reprocessing of the flare into IR, optical and UV emission lines provides us with multiple new diagnostics of the properties of any gaseous material in the vicinity of the black hole (including the disrupted star itself) and in the host galaxy. First candidate events of this kind have been reported recently.

Slow-blue nuclear hypervariables in PanSTARRS-1

“…Good candidates have been found for such events, both in the optical/UV (Gezari et al 2008(Gezari et al , 2009van Velzen et al 2011;Chornock et al 2014) and in X-rays (Brandt, Pounds & Fink 1995;Grupe et al 1995;Bade, Komossa & Dahlem 1996;Halpern, Gezari & Komossa 2004;Komossa et al 2004;Komossa 2012). Could our slow-blue transients be examples of TDEs?…”

Hard X-ray luminosity function of tidal disruption events: First results from the MAXI extragalactic survey

“…Some of TDEs have also been detected in the optical and UV bands (e.g., Gezari et al 2006Gezari et al , 2008Gezari et al , 2012Arcavi et al 2014;Holoien et al 2014;van Velzen et al 2011). Since the first detection of a TDE, which occurred in NGC 5905 (Bade et al 1996), a few tens of X-ray TDEs have been identified (Komossa 2012). The identifications of TDEs were mainly based on their variability characteristics, such as a large amplitude and the unique decline law of the light curve (e.g., Komossa & Bade 1999), which are supported by both analytic solutions (Rees 1988;Phinney 1989) and numerical simulations (e.g., Evans & Kochanek 1989).…”

Spoon-feeding an active galactic nucleus

“…Several authors [7], [8], [9], [10] interpreted this emission as coming from the total tidal disruption of a star orbiting around the central massive black hole (∼ 3 × 10 5 M [11]) of the galaxy, even if IC 3599 is a low-luminosity active galactic nucleus (AGN). Indeed in AGNs it is difficult to distinguish between variability coming from the galaxy itself and variability induced by the disruption of a star, even if in AGNs the presence of a pre-existent accretion disk enhances the probability to have tidal disruption events [12], [13].…”