Revision D - Annotated image with Original image mouse-hover
Revision B - Starless image with Inverse Monochrome mouse-hover

The supernova remnant:

SNR G206.9+02.3, is in the lower part of the image - identified by its blue highlights (OIII emission). The supernova event took place sometime 15,000 to 60,000 years ago. Its distance is estimated at 3,000 to 7,000 light years. Distance and age has a large variation of estimates. Part of the issue is the huge Monogem Ring which is pervasive across this region. Later studies attempt to ‘disentangle’ individual Monogem Ring’s radiation from that of the more distant individual SNR’s.

The 1986 study by D.A. Leahy pegged the estimates at 9,000 light years for distance and 60,000 years for age. Similar study in 2014 by Ambrocio-Cruz et al. showed about 7,000 light years for distance and 60,000 years age. Both studies were exclusively on SNR G206.9+02.3 and also concluded this SNR was in its radiative phase (or final stage of life).

The 2020 study by He Zhao et al. used the approach of taking line of sight stars (whose distance is known) leading toward various SNR’s and evaluating their extinction due to intervening ISM. This was pegged to the SNR extinction to get an SNR distance measurement. This method yielded the lowest distance estimate - about 3,000 light years.

The 2024 study by J. R. Knies et al. uses the ROSITA imaging data (pektrum-Röntgen-Gamma platform at L2 Lagrange). X-ray data resolution from this survey has significantly improved. This data resulted in the lower age estimate in the range.

Annotation :

The annotation has been relatively straight forward. However, there is one interesting item - The “galaxy” UGC 3543.

This image is in the ‘Zone of Avoidance’. A 1995 “introduction to a series of papers” by Weinberger et al. summarized various paper on this Zone (ZOA) in order to update existing database information. Indeed, there is the assertion that as better observing techniques become available - particularly multi-wavelength observing - the ZOA may eventually be “eliminated”. Not only are there new extra galactic objects being added, but also some objects are misidentified as being extra galactic. Galaxy UGC 3543 (MCG+01-18-002) is one object re-designated as a reflection nebula.

So now it is a reflection nebula with a galaxy ID designation. But it makes sense. There is a NED measurement for redshift (which is a close to zero as possible) which means this ‘extra galactic’ object would be within the Milky Way.

Website links to Pan and zoom with Navigation Pane (upper right) and full screen view (upper left buttons):

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