A newborn spider system at the core of a radio shell: Evidence of a low-energy supernova

In a search for radio nebulae with a low surface brightness within the ASKAP-EMU survey, we discovered a faint radio shell, G289.6+5.8, and its central point radio source at the position of the soft γ -ray source IGR J11187-5438. The central radio source is spatially coincident with a previously known low-mass X-ray binary (LMXB) with an M-type donor star. However, the newly determined Gaia DR3 distance of 267 pc and correspondingly low X-ray luminosity (3×10 31 erg s −1 ) cast doubt on the LMXB classification. Neither radio nor X-ray pulsations are detected. Chance alignments between radio shell, central radio source, optical star, γ -ray, and X-ray sources appear unlikely. By combining all currently available evidence, we conclude that G289.6+5.8 is a remnant of a low-energy core-collapse explosion of an intermediate-mass star (~8M ⊙ ) in a binary system with an M-type secondary that remained bound after the explosion. In this scenario, G289.6+5.8 is a supernova remnant, while the central γ - and X-ray source is associated with a young neutron star whose pulsar wind interacts with its M-type stellar companion, making IGR J11187-5438 a nascent spider-type X-ray binary.