The first VLBI image of the young, oxygen-rich supernova remnant in NGC 4449

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 × 40 mas, corresponding to (3.7 × 2.3) × 1018 (D/3.8 Mpc) cm. We also present a new, high signal‐to‐noise ratio 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.

Flux density variations of radio sources in M82

“…VLBI observations of 41.95+57.5 in November 1998 and February 2001 shows the source to be expanding at a rate of ∼2000±500 km s The unusually luminous radio supernova 1986J in NGC891 and 41.95+57.5 show some distinct similarities. Both sources display an asymmetric radio structure on milliarcsecond scales, modest expansion velocities, relatively high initial radio luminosities and a power-law flux density decay (Bietenholz et al 2010). Both the possible decrease in apparent angular size and the small deviation from the historical flux density decline of 41.95+57.5 in these recent 5 GHz flux density measurements are consistent with the potential appearance of a new higher frequency central component within the shell.…”

Planetary Nebulae and H ii Regions in the Starburst Irregular Galaxy NGC 4449 from LBT MODS Data

“…Given the evidence for a conspicuous population of WR stars in NGC 4449 (Martin & Kennicutt 1997;Bietenholz et al 2010;Srivastava et al 2014;Sokal et al 2015, see also Section 5), local pollution from WR ejecta enriched in N is an attractive possibility to explain the observed behaviour. Although significant amounts of N and C are expected to be injected by WR stars on theoretical grounds (e.g.…”

A NEWLY RECOGNIZED VERY YOUNG SUPERNOVA REMNANT IN M83,,

“…include the extraordinary young SNR in NGC 4449 (Milisavljevic & Fesen 2008), thought to be of order 70 years post-explosion (Bietenholz et al 2010), Cassiopeia A in our Galaxy (see Fig. 14 of Milisavljevic et al (2012) for an 'integrated' spectrum of this object), which dates to ∼1680 AD, and even 1E0102-7219 in the Small Magellanic Cloud, which is still ejecta-dominated even ∼2000 years post-explosion (Blair et al 2000;Finkelstein et al 2006;Vogt & Dopita 2010).…”