XMM-Newton detection of Nova Muscae 1991 in Quiescence
  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. 
F.K. Sutaria, U. Kolb, P.A. Charles, J.P. Osborne, E. Kuulkers, J.   Casares, E.T. Harlaftis, T. Shahbaz, M.D. Still, P.J. W...