A two-component jet model for the tidal disruption event Swift J164449.3+573451

TL;DR

This paper proposes a two-component jet model for the tidal disruption event Swift J1644+57, explaining early and late radio and X-ray emissions through an inner relativistic jet and an outer trans-relativistic jet, matching observed data.

Contribution

The study introduces a self-consistent two-component jet model that explains the complex radio and X-ray emission evolution in the tidal disruption event.

Findings

Inner jet is relativistic with Lorentz factor ~15.

Outer jet is trans-relativistic with Lorentz factor ≤ 1.2.

Model explains late-time radio re-brightening without late engine activity.

Abstract

We analyze both the early and late time radio and X-ray data of the tidal disruption event Swift J1644+57. The data at early times ($\lesssim 5$ days) necessitates separation of the radio and X-ray emission regions, either spatially or in velocity space. This leads us to suggest a two component jet model, in which the inner jet is initially relativistic with Lorentz factor $\Gamma \approx 15$, while the outer jet is trans-relativistic, with $\Gamma \lesssim 1.2$. This model enables a self-consistent interpretation of the late time radio data, both in terms of peak frequency and flux. We solve the dynamics, radiative cooling and expected radiation from both jet components. We show that while during the first month synchrotron emission from the outer jet dominates the radio emission, at later times radiation from ambient gas collected by the inner jet dominates. This provides a natural explanation to the observed re-brightening, without the need for late time inner engine activity. After 100 days, the radio emission peak is in the optically thick regime, leading to a decay of both the flux and peak frequency at later times. Our model's predictions for the evolution of radio emission in jetted tidal disruption events can be tested by future observations.