  About a dozen substellar companions orbiting young stellar objects or
pre-main sequence stars at several hundred au have been identified in the last
decade. These objects are interesting both due to the uncertainties surrounding
their formation, and because their large separation from the host star offers
the potential to study the atmospheres of young giant planets and brown dwarfs.
Here, we present X-shooter spectroscopy of SR 12 C, a $\sim\,2\,$Myrs young
brown dwarf orbiting SR 12 at an orbital separation of 1083 au. We determine
the spectral type, gravity, and effective temperature via comparison with
models and observational templates of young brown dwarfs. In addition, we
detect and characterize accretion using several accretion tracers. We find SR
12 C to be a brown dwarf of spectral type L0 $\pm$ 1, $\log$ g = 4 $\pm$ 0.5,
an effective temperature of 2600 $\pm$ 100 K. Our spectra provide clear
evidence for accretion at a rate of $\sim$ $10^{-10}$ $M_{\odot}yr^{-1}$. This
makes SR 12 one of the few sub-stellar companions with a reliable estimate for
its accretion rate. A comparison of the ages and accretion rates of sub-stellar
companions with young isolated brown dwarfs does not reveal any significant
differences. If further accretion rate measurements of a large number of
substellar companions can confirm this trend, this would hint towards a similar
formation mechanism for substellar companions at large separations and isolated
brown dwarfs.
