Compact source resolution and rapid variability in Arp220

TL;DR

This study uses multi-epoch VLBI observations to analyze compact radio sources in Arp220, revealing properties consistent with supernovae and remnants, and identifying highly variable sources with potential superluminal motion, suggesting possible new source classes or AGN activity.

Contribution

It extends the luminosity-diameter relation for SNRs to smaller sources and identifies candidate transition objects and variable sources with superluminal motion in Arp220.

Findings

Most sources are consistent with SNe or SNRs.

Detection of sources with superluminal motion (~4c).

Identification of a probable SN/SNR transition candidate.

Abstract

We present multi-epoch global VLBI observations at 2 cm, 3.6 cm and 6 cm of the compact radio sources in Arp220. We resolve many sources and estimate sizes, expansion velocities and source classes. We find most source properties are consistent with them being either radio supernovae (SNe) or supernova remnants (SNRs). We extend the luminosity-diameter relation for SNRs to very small sources and argue this supports models where shell magnetic fields are internally amplified. We also detect one probable SN/SNR transition object candidate and three highly variable sources with possible superluminal motion (approximately 4c) of jet-like features near rapidly varying almost stationary components. These enigmatic sources, which show similarities to the recently discovered superluminal source in M82, might be associated with an AGN or a new radio source class (e.g. intermediate-mass black holes or micro-blazars).