  The soft X-ray transient GU Mus has been detected by XMM-Newton in the
quiescent state. The source is very faint, with a 0.5-10.0 keV unabsorbed flux
of $\simeq 1.1 \times 10^{-14}$ ergs cm$^{-2}$ s$^{-1}$. The spectra is well
fit by an absorbed powerlaw with a photon index of $ \alpha = 1.6 \pm 0.4$,
close to the value seen when the source was in the low/hard state in Aug. 1991.
  From our observed luminosity, it seems unlikely that the quiescent state
emission is dominated by coronal X-rays from the secondary. The flux also
appears to be in agreement with the ADAF model of BH-transients in quiescence.
