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Description
The nearby ultra-luminous infrared galaxy (ULIRG) Arp 220 is an excellent laboratory for studies of extreme astrophysical environments. For 20 years, Very Long Baseline Interferometry (VLBI) has been used to monitor a population of compact sources thought to be supernovae (SNe), supernova remnants (SNRs) and possibly active galactic nuclei (AGNs). SNe and SNRs are thought to be the sites of relativistic particle acceleration powering the star formation induced radio emission, and are hence important for studies of e.g. the origin of the FIR-radio correlation. In this work we aim for a self-consistent analysis of a large collection of Arp 220 continuum VLBI data sets. With more data and improved consistency in calibration and imaging, we aim to detect more sources and improve source classifications with respect to previous studies. Furthermore, we aim to increase the number of sources with robust size estimates, to analyse the compact source luminosity function (LF), and to search for a luminosity-diameter (LD) relation within Arp 220. Using new and archival VLBI data spanning 20 years, we obtain 23 high-resolution radio images of Arp 220 at wavelengths from 18cm to 2cm. From model-fitting to the images we obtain estimates of flux densities and sizes of all detected sources. The sources are classified in groups according to their observed lightcurves, spectra and sizes. We fit a multi-frequency supernova lightcurve model to the object brightest at 6cm to estimate explosion properties for this object.
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