Abstract
We explore the temporal structure of tidal disruption events pointing out the corresponding transitions in the lightcurves of the thermal accretion disk and of the jet emerging from such events. The hydrodynamic time scale of the disrupted star is the minimal time scale of building up the accretion disk and the jet and it sets a limit on the rise time. This suggest that Swift J1644+57, that shows several flares with a rise time as short as a few hundred seconds could not have arisen from a tidal disruption of a main sequence star whose hydrodynamic time is a few hours. The disrupted object must have been a white dwarf. A second important time scale is the Eddington time in which the accretion rate changes form super to sub Eddington. It is possible that such a transition was observed in the light curve of Swift J2058+05. If correct this provides intersting constraints on the parameters of the system.
Highlights
Tidal disruption events (TDE) of s stellar mass object by a massive black hole are a classical transient phenomenon that involves numerous time scales: (i) the gravitational time scale of the massive black hole (ii) the orbital period at the tidal radius, which equals the hydrodynamic time scale of the disrupted star, (iii) the orbital period at the innermost semi-major axis of the disrupted stellar material on which the accretion rate peaks, (iv) the transition from super so sub Eddington accretion and (v) the transition from radiation dominated inner disk region to gas pressure dominated
For typical parameters these values range from a few dozen seconds to several years, all but the second depend strongly on the black hole’s mass. They provide invaluable information concerning the system. We examine these times scales and their implications to the interpretation of the observations of Swift J1644+57 and J2058+05
The shortest time scale expected in a TDE is the orbital period, Porb, of the tidal radius, RT
Summary
Tidal disruption events (TDE) of s stellar mass object by a massive black hole are a classical transient phenomenon that involves numerous time scales: (i) the gravitational time scale of the massive black hole (ii) the orbital period at the tidal radius, which equals the hydrodynamic time scale of the disrupted star, (iii) the orbital period at the innermost semi-major axis of the disrupted stellar material on which the accretion rate peaks, (iv) the transition from super so sub Eddington accretion and (v) the transition from radiation dominated inner disk region to gas pressure dominated For typical parameters these values range from a few dozen seconds to several years, all but the second depend strongly on the black hole’s mass. Numerical simulations of the disruption of a main sequence star by a 106 M black hole [6] show a rather continuous accretion rate with a rise time of a few times sec and an overall duration of a few times sec, as expected from these analytic estimates
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