VLT/ERIS observations of the V960 Mon system: a dust-embedded substellar object formed by gravitational instability?

V960~Mon is an FU Orionis object that shows strong evidence of a gravitationally unstable spiral arm that is fragmenting into several dust clumps. We report the discovery of a new substellar companion candidate around this young star, identified in high-contrast $L'$-band imaging with VLT/ERIS. The object is detected at a projected separation of $0.898 \pm 0.01$ arcseconds with a contrast of $(8.39 \pm 0.07) \times 10^{-3}$. The candidate lies close to the clumps previously detected in the sub-mm (at 1.3 mm) and is co-located with extended polarized IR signal from scattered stellar irradiation, suggesting it is deeply embedded. The object is undetected in the SPHERE $H$-band total intensity, placing an upper mass limit of $\sim38~M_\mathrm{Jup}$ from the contrast curve. Using evolutionary models at an assumed age of 1~Myr, we estimate a mass of $\sim660~M_\mathrm{Jup}$ from the L' brightness; however, this value likely includes a significant contribution from a disk around the companion. The discrepancy between near- and mid-infrared results again suggests the source is deeply embedded in dust. This candidate may represent an actively accreting, disk-bearing substellar object in a young, gravitationally unstable environment.