# Detection of Extensive Optical Emission from the Extremely Radio Faint Galactic Supernova Remnant G182.4+4.3

## TL;DR

This study reveals extensive optical emission from the faint Galactic supernova remnant G182.4+4.3, indicating slow shocks and an older age, with minimal X-ray and radio emissions due to its low shock velocity and low-density environment.

## Contribution

First detailed optical imaging and spectral analysis of G182.4+4.3, showing its large size, old age, and shock properties, expanding understanding of faint supernova remnants.

## Key findings

- Optical emission is extensive and complex, with diffuse filaments.
- Remnant's optical emission mainly from slow shocks (<70 km/s).
- Estimated age of ~40 kyr and size of ~50 pc at 4 kpc distance.

## Abstract

Wide-field Halpha images of the radio faint Galactic supernova remnant G182.4+4.2 reveal a surprisingly extensive and complex emission structure, with an unusual series of broad and diffuse filaments along the remnant's southwestern limb. Deep [O III] 5007 images reveal no appreciable remnant emission with the exception of a single filament coincident with the westernmost of the broad southwest filaments. The near total absence of [O III] emission suggests the majority of the remnant's optical emission arises from relatively slow shocks (<70 km/s), consistent with little or no associated X-ray emission. Low-dispersion optical spectra of several regions in the remnant's main emission structure confirm a lack of appreciable [O III] emission and indicate [S II]/Halpha line ratios of 0.73 - 1.03, consistent with a shock-heated origin. We find G182.4+4.2 to be a relatively large (d~50 pc at 4 kpc) and much older (age ~40 kyr) supernova remnant than previously estimated, whose weak radio and X-ray emissions are related to its age, low shock velocity, and location in a low density region some 12 kpc out from the Galactic centre.