1111.2802 (Julian H. Krolik et al.)

Jets from Tidal Disruptions of Stars by Black Holes    [PDF]

Julian H. Krolik, Tsvi Piran

Tidal disruption of main sequence stars by black holes has generally been
thought to lead to a signal dominated by UV emission. If, however, the black
hole spins rapidly and the poloidal magnetic field intensity on the black hole
horizon is comparable to the inner accretion disk pressure, a powerful jet may
form whose luminosity can easily exceed the thermal UV luminosity. When the jet
beam points at Earth, its non-thermal luminosity can dominate the emitted
spectrum. The thermal and non-thermal components decay differently with time.
In particular, the thermal emission should remain roughly constant for a
significant time after the period of maximum accretion, beginning to diminish
only after a delay, whereas after the peak accretion rate, the non-thermal jet
emission decays, but then reaches a plateau. Both transitions are tied to a
characteristic timescale $t_{\rm Edd}$ at which the accretion rate falls below
Eddington. Making use of this timescale in a new parameter-inference formalism
for tidal disruption events with significant emission from a jet, we analyze
the recent flare source Swift J2058. It is consistent with an event in which a
main sequence solar-type staris disrupted by a black hole of mass $\sim 4
\times 10^7 M_{\odot}$. The beginning of the flat phase in the non-thermal
emission from this source can possibly be seen in the late-time lightcurve.
Optical photometry over the first $\simeq 40$ d of this flare is also
consistent with this picture, but is only weakly constraining because the
bolometric correction is very uncertain. We suggest that future searches for
main sequence tidal disruptions use methods sensitive to jet radiation as well
as to thermal UV radiation.

View original: http://arxiv.org/abs/1111.2802