EMU Detection of a Large and Low Surface Brightness Galactic SNR G288.8-6.3

We present the serendipitous detection of a new Galactic Supernova Remnant (SNR), G288.8-6.3 using data from the Australian Square Kilometre Array Pathfinder (ASKAP)-Evolutionary Map of the Universe (EMU) survey. Using multi-frequency analysis, we confirm this object as an evolved Galactic SNR at high Galactic latitude with low radio surface brightness and typical SNR spectral index of $\alpha =-0.41\pm 0.12$. To determine the magnetic field strength in SNR G288.8-6.3, we present the first derivation of the equipartition formulae for SNRs with spectral indices $\alpha >-0.5$. The angular size is $1.\text{\hspace{0.17em}⁣}{}^{\circ }8\times 1.\text{\hspace{0.17em}⁣}{}^{\circ }6$ $(107.\text{\hspace{0.17em}⁣}{}^{\mathrm{\prime }}6\times 98.\text{\hspace{0.17em}⁣}{}^{\mathrm{\prime }}4)$ and we estimate that its intrinsic size is $\sim 40$pc which implies a distance of $\sim 1.3$kpc and a position of $\sim 140$pc above the Galactic plane. This is one of the largest angular size and closest Galactic SNRs. Given its low radio surface brightness, we suggest that it is about 13000 years old.