CHANG-ES V: Nuclear Radio Outflow in a Virgo Cluster Spiral after a Tidal Disruption Event

TL;DR

This study reports on the detection of a nuclear radio outflow in galaxy NGC 4845, linked to a tidal disruption event, revealing a variable, peaked-spectrum core likely driven by a jet or cone, with implications for understanding TDE-related outflows.

Contribution

First detailed radio observation of a TDE in NGC 4845 showing a variable, peaked-spectrum core consistent with a jet or outflow, linking radio and X-ray emissions.

Findings

Core exhibits a GHz-peaked spectrum dominated by synchrotron self-absorption.

Core variability and spectral evolution suggest adiabatic expansion of an outflow.

Potential to resolve a young radio jet with VLBI observations.

Abstract

We have observed the Virgo Cluster spiral galaxy, NGC~4845, at 1.6 and 6 GHz using the Karl G. Jansky Very Large Array, as part of the `Continuum Halos in Nearby Galaxies -- an EVLA Survey' (CHANG-ES). The source consists of a bright unresolved core with a surrounding weak central disk (1.8 kpc diameter). The core is variable over the 6 month time scale of the CHANG-ES data and has increased by a factor of $\approx$ 6 since 1995. The wide bandwidths of CHANG-ES have allowed us to determine the spectral evolution of this core which peaks {\it between} 1.6 and 6 GHz (it is a GigaHertz-peaked spectrum source).We show that the spectral turnover is dominated by synchrotron self-absorption and that the spectral evolution can be explained by adiabatic expansion (outflow), likely in the form of a jet or cone. The CHANG-ES observations serendipitously overlap in time with the hard X-ray light curve obtained by Nikolajuk \& Walter (2013) which they interpret as due to a tidal disruption event (TDE) of a super-Jupiter mass object around a $10^5\, M_\odot$ black hole. We outline a standard jet model, provide an explanation for the observed circular polarization, and quantitatively suggest a link between the peak radio and peak X-ray emission via inverse Compton upscattering of the photons emitted by the relativistic electrons. We predict that it should be possible to resolve a young radio jet via VLBI as a result of this nearby TDE.