Disk Winds as an Explanation for Slowly Evolving Temperatures in Tidal Disruption Events

Among the many intriguing aspects of optically discovered tidal disruption events (TDEs) is that their temperatures are lower than predicted and that the temperature does not evolve as rapidly with a decreasing fallback rate as would be expected in standard disk theory. We show that this can be explained qualitatively using an idea proposed by Laor & Davis in the context of normal active galactic nuclei: that larger accretion rates imply stronger winds and thus that the accretion rate through the inner disk only depends weakly on the inflow rate at the outer edge of the disk. We also show that a reasonable quantitative agreement with data requires that, as has been suggested in recent papers, the characteristic radius of the tidal stream is approximately equal to the semimajor axis of the most bound orbit of the debris rather than twice the pericenter distance, which would be expected from circularization without rapid angular momentum redistribution. If this explanation is correct, it suggests that the evolution of TDEs may test both non-standard disk theory and the details of the interactions of the tidal stream.