External inverse-Compton emission from jetted tidal disruption events

TL;DR

This paper models the inverse-Compton emission from relativistic jets in tidal disruption events, explaining observed X-ray and gamma-ray luminosities by scattering of thermal radiation from super-Eddington winds.

Contribution

It introduces a model linking thermal optical-UV spectra to inverse-Compton X-ray emission in jetted TDEs, providing constraints on jet and wind parameters based on observations.

Findings

The optical-UV blackbody component originates from super-Eddington wind.

Inverse-Compton scattering explains the observed X-ray luminosity and spectrum.

Jet Lorentz factor is estimated to be around 5-10.

Abstract

The recent discoveries of Swift J1644+57 and J2058+05 show that tidal disruption events (TDEs) can launch relativistic jets. Super-Eddington accretion produces a strong radiation field of order Eddington luminosity. In a jetted TDE, electrons in the jet will inverse-Compton scatter the external radiation field from the accretion disk and wind. Motivated by observations of thermal optical-UV spectra in Swift J2058+05 and several other TDEs, we assume the spectrum of the external radiation field intercepted by the relativistic jet to be blackbody. Hot electrons in the jet scatter this thermal radiation and produce luminosities 10^45-10^48 erg/s in the X/gamma-ray band. This model of thermal plus inverse-Compton radiation is applied to Swift J2058+05. First, we show that the blackbody component in the optical-UV spectrum most likely has its origin in the super-Eddington wind from the disk. Then, using the observed blackbody component as the external radiation field, we show that the X-ray luminosity and spectrum are consistent with the inverse-Compton emission, under the following conditions: (1) the jet Lorentz factor is ~5-10; (2) electrons in the jet have a powerlaw distribution with minimum Lorentz factor ~1 and powerlaw index p = 2.4; (3) the wind is mildly relativistic (Lorentz factor >~1.5) and has isotropic-equivalent mass-loss rate ~5 M_sun/yr. We describe the implications for jet composition and the radius where jet energy is converted to radiation.