The expansion of SN 2008iz in M82

TL;DR

This paper reports on VLBI radio observations of supernova SN 2008iz in M82, revealing a self-similarly expanding shell with a central compact component, and discusses the marginally decelerated expansion and modeling challenges.

Contribution

First VLBI imaging of SN 2008iz showing shell expansion and a central compact source, with analysis of expansion dynamics and modeling constraints.

Findings

Shell-like structure with circular symmetry observed

Expansion is marginally decelerated (m=0.89)

Presence of a compact central component with steep spectrum

Abstract

We present first results from the ongoing radio monitoring of SN 2008iz in M82. The VLBI images reveal a shell-like structure with circular symmetry, which expands in a self-similar way. There is strong evidence of a compact component with a steep spectrum at the center of the shell. The expansion curve obtained from our VLBI observations is marginally decelerated (m = 0.89) and can be modeled simultaneously with the available radio light curves. While the results of this simultaneous fitting are not conclusive (i.e. different combinations of values of the magnetic field, CSM density profile, and electron energy distribution, provide fits to the available data with similar quality), additional observations should allow a more robust and detailed modeling.