Distance and Evolutionary States of Supernova Remnant G18.9-1.1 and Candidate G28.6+0.0

TL;DR

This study determines the distances, ages, and explosion energies of supernova remnants G18.9-1.1 and G28.6+0.0 using spectral analysis, revealing their evolutionary states and environmental conditions.

Contribution

It provides new kinematic distances, ages, and explosion energies for G18.9-1.1 and G28.6+0.0, applying spectral and Sedov models to better understand their evolution.

Findings

G18.9-1.1 is at 2.1 kpc with an age of ~3700-4700 years.

G28.6+0.0 is at 9.0 kpc with an age range of 600-6000 years.

G18.9-1.1 has an explosion energy of about 3×10^{50} erg.

Abstract

HI spectra of the supernova remnant G18.9-1.1 and the supernova remnant candidate G28.6+0.0 are analyzed. We compared the spectra to $^{13}$CO emission spectra and to spectra of HII regions in the area to determine kinematic distances. G18.9-1.1 is at 2.1$\pm$0.4 kpc and G28.6+0.0 is at 9.0$\pm$0.3 kpc from the Sun. Using published X-ray spectra of G18.9-1.1, we apply supernova remnant models for shocked-ISM temperature and emission measure. We find that G18.9-1.1 has a low, but not atypical, explosion energy of $\simeq$3$\times$10$^{50}$ erg and is in a low density region of the ISM, $\simeq$0.1 cm$^{-3}$. It has age $\simeq$3700 yr if the ejecta mass is 1.4 M$_{\odot}$, typical of Type Ia SNe, or $\simeq$4700 yr if the ejecta mass is 5 M$_{\odot}$ typical of core-collapse SN. The candidate G28.6+0.0 does not have reported X-ray emission, so we apply a basic Sedov model. The Sedov age is $\simeq$600 yr if the ISM density is 1 cm$^{-3}$ but could be as old as $\simeq$6000 yr if the ISM density is as high as 100 cm$^{-3}$.