Late-time Radio Flares in Tidal Disruption Events

TL;DR

This paper explains late-time radio flares in tidal disruption events as a consequence of a flattening density profile outside the Bondi radius, with the model fitting observed light curves and constraining black hole and outflow properties.

Contribution

It introduces a model linking late-time radio flares to the density profile outside the Bondi radius, providing a method to estimate black hole and outflow parameters from radio observations.

Findings

Late-time radio flares are explained by a flattening density profile outside the Bondi radius.

The model fits observed light curves and constrains black hole and outflow masses.

The density profile slope influences the presence of early-time radio peaks.

Abstract

Radio monitoring unveiled late (hundreds to a thousand days) radio flares in a significant fraction of tidal disruption events. We propose that these late-time radio flares are a natural outcome if the surrounding density profile flattens outside the Bondi radius. At the Bondi radius, the outflow is optically thin (above a few GHz) to synchrotron self-absorption. As more and more material is swept up, the radio emission rises asymptotically as $\propto t^3$ until the outflow begins to decelerate. A Detection of such a rise and a late-time maximum constrains the black hole mass and the mass and energy of the radio-emitting outflow. We show that this model can give reasonable fits to some observed light curves, leading to reasonable estimates of the black hole and outflow masses. We also find that the slope of the density profile within the Bondi radius determines whether an early-time ($\sim10^2\,\rm days$) radio peak exists.