XMM search for $X$-ray emission from the black hole candidate   MACHO-96-BLG-5
  MACHO-96-BLG-5 is a microlensing event observed towards the bulge of the Galaxy with exceptionally long duration of $\sim 970$ days. The microlensing parallax fit parameters were used to estimate the lens mass $M=6^{+10}_{-3}$ M$_{\odot}$ and its distance $d$ which results to be in the range 0.5 kpc - 2 kpc. The upper limit on the absolute brightness for main-sequence stars of the same mass is less than 1 $L_{\odot}$ so that the lens is a good black hole candidate. If it is so, the black hole would accrete by interstellar medium thereby emitting in the $X$-ray band. Here, the analysis of an {\it XMM} deep observation towards MACHO-96-BLG-5 lens position is reported. Only an upper limit (at 99.8% confidence level) to the $X$-ray flux from the lens position of $9.10\times 10^{-15}$-- $1.45\times 10^{-14}$ erg cm$^{-2}$ s$^{-1}$ in the energy band $0.2-10$ keV has been obtained from that deep observation allowing to constrain the putative black hole accretion parameters. 
A. A. Nucita, F. De Paolis, G. Ingrosso, D. Elia, J. de Plaa, J. S.   Kaastra