Probing the structure of the outflow in the tidal disruption flare Sw J1644+57 with long-term radio emission

TL;DR

This paper analyzes long-term radio data from the tidal disruption event Sw J1644+57, revealing the outflow's transition from a conical to cylindrical shape, indicating possible jet collimation and the onset of an active galactic nucleus.

Contribution

It provides detailed evolution of the outflow structure in Sw J1644+57, demonstrating a transition from conical to cylindrical geometry through multi-epoch radio spectral analysis.

Findings

Outflow transitions from conical to cylindrical shape over time

Jet collimation likely caused by pressure from the shocked cocoon

Evidence suggests Sw J1644+57 signals the beginning of an AGN

Abstract

The recently discovered high-energy transient Sw J1644+57 is thought to arise from the tidal disruption of a passing star by a dormant massive black hole. The long-term, bright radio emission of Sw J1644+57 is believed to result from the synchrotron emission of the blast wave produced by an outflow expanding into the surrounding medium. Using the detailed multi-epoch radio spectral data, we are able to determine the total number of radiating electrons in the outflow at different times, and further the evolution of the cross section of the outflow with time. We find that the outflow gradually transits from a conical jet to a cylindrical one at later times. The transition may be due to collimation of the outflow by the pressure of the shocked jet cocoon that forms while the outflow is propagating in the ambient medium. Since cylindrical jets usually exist in AGNs and extragalactic jets, this may provide independent evidence that Sw J1644+57 signals the onset of an AGN.