SNR G182.4+4.3 – Deep Sky Collective
SNR G182.4+4.3 is a supernova remnant in the constellation Auriga, sitting roughly 13,000 light-years away and spanning about 163 light-years, or 50 arcminutes, across. It’s not a well-known target. First detected in radio wavelengths in 1998, its optical Ha and SII filaments weren’t confirmed until 2012, and the first OIII signal only appeared in the literature in 2019. When we began imaging it in December 2024, just three amateur images existed online, none of which went deep enough to show the full extent of the remnant.
What the data revealed
With 427 hours and 24 minutes of total integration across 12 contributors, this is the deepest image of this field to date. The breakdown: 144 hours of Ha, 130 hours of OIII, 53 hours of SII, and the remainder in LRGB.
One of the goals from the start was to capture the full OIII loop, which had never been properly shown in amateur imaging. We believe we achieved something very close to it. The main OIII emission in the south-west is notably atypical: the filament sits further out than the Ha emission in that region, lying instead on the remnant’s brightest radio filament. According to Fesen et al., this kind of emission profile may indicate significant post-shock cooling, potentially a sign that the remnant is transitioning into the radiative phase, where shock-heated gas cools rapidly and expansion begins to slow.
Ha and SII showed near-identical structure and intensity throughout, with a SII/Ha ratio of around 1.0 across most of the emissions. In the final image, SII was blended in as yellow, producing an orangey-red tone that keeps the aesthetic readable while still conveying the spectral information.
Beyond the SNR itself, the field contains a notable shift in IFN density running diagonally across the frame, likely a result of the remnant’s position slightly offset from the galactic plane. The result is IFN dominating one corner and Ha cirrus the other, with the SNR anchoring the centre.
Three versions
This project produced three independent edits of the same dataset, each approaching the processing differently. Steeve Body’s edit is the main published version, with Nicolas Puig’s OIII continuum subtraction version and Alpha’s edit also available.
Integration
L: 47h 54m / R: 15h 06m / G: 20h 12m / B: 16h 18m / Ha: 144h 30m / OIII: 130h 24m / SII: 53h 00m / Total: 427h 24m
Credits
Tim Schaeffer (coordination), Jasper Capel (stacking and photography), Steeve Body (editor), Nicolas Puig (editor), Alpha (editor), Carl Björk (stacking support and photography). Photographers: Akash Jain, Logan Carpenter, Florent Herrbach, Kevin Morefield, John Dziuba, Jim Matzger.
Full image in gallery at https://deepskycollective.com/gallery.