The First VLBI Image of the Young, Oxygen-Rich Supernova Remnant in NGC 4449

TL;DR

This paper presents the first high-resolution VLBI radio image of the young, oxygen-rich supernova remnant SNR 4449-1 in NGC 4449, revealing its morphology, size, and age, and providing insights into its shock interaction with the surrounding medium.

Contribution

It provides the first well-resolved VLBI image of SNR 4449-1, estimates its age around 70 years, and analyzes its morphology and shock interaction with circumstellar material.

Findings

Remnant's radio morphology shows two bright ridges, similar to barrel-shaped remnants.

Angular size of 65 x 40 mas corresponds to a physical size of approximately 3.7 x 2.3 x 10^{18} cm.

Estimated explosion date around 1940, making the remnant about 70 years old.

Abstract

We report on sensitive 1.4-GHz VLBI radio observations of the unusually luminous supernova remnant SNR 4449-1 in the galaxy NGC 4449, which gave us the first well-resolved image of this object. The remnant's radio morphology consists of two approximately parallel bright ridges, suggesting similarities to the barrel shape seen for many older Galactic supernova remnants or possibly to SN 1987A. The angular extent of the remnant is 65 x 40 mas, corresponding to (3.7 x 2.3) x 10^{18} (D/3.8 Mpc) cm. We also present a new, high signal-to-noise optical spectrum. By comparing the remnant's linear size to the maximum velocities measured from optical lines, as well as using constraints from historical images, we conclude that the supernova explosion occurred between ~1905 and 1961, likely around 1940. The age of the remnant is therefore likely ~70 yr. We find that SNR 4449-1's shock wave is likely still interacting with the circumstellar rather than interstellar medium.