Swift J1644+57: an Ideal Test Bed of Radiation Mechanisms in a Relativistic Super-Eddington Jet

TL;DR

This paper analyzes multiwavelength observations of the TDE Sw J1644+57 to identify the radiation mechanisms in its relativistic super-Eddington jet, ruling out several processes and highlighting the role of magnetic reconnection and electron acceleration.

Contribution

It provides a comprehensive evaluation of possible radiation mechanisms in a TDE jet, emphasizing the importance of continuous electron acceleration and magnetic reconnection in a Poynting flux dominated jet.

Findings

Synchrotron and external-inverse-Compton processes are consistent with data.

Many radiation mechanisms like SSC, photospheric, and proton synchrotron are ruled out.

Magnetic reconnection likely drives continuous electron acceleration.

Abstract

Within the first 10 days after Swift discovered the jetted tidal disruption event (TDE) Sw J1644+57, simultaneous observations in the radio, near-infrared, optical, X-ray and gamma-ray bands were carried out. These multiwavelength data provide a unique opportunity to constrain the emission mechanism and make-up of a relativistic super-Eddington jet. We consider an exhaustive variety of radiation mechanisms for the generation of X-rays in this TDE, and rule out many processes such as SSC, photospheric and proton synchrotron. The infrared to gamma-ray data for Sw J1644+57 are consistent with synchrotron and external-inverse-Compton (EIC) processes provided that electrons in the jet are continuously accelerated on a time scale shorter than ~1% of the dynamical time to maintain a power-law distribution. The requirement of continuous electron acceleration points to magnetic reconnection in a Poynting flux dominated jet. The EIC process may require fine tuning to explain the observed temporal decay of the X-ray lightcurve, whereas the synchrotron process in a magnetic jet needs no fine tuning for this TDE.