Chandra detection of XTE J1650-500 in quiescence and the minimum luminosity of black hole X-ray binaries

The Galactic black hole X-ray binary XTE J1650-500 entered a quiescent regime following the decline from the 2001-2002 outburst that led to its discovery. Here we report on the first detection of its quiescent counterpart in a 36 ks observation taken in 2007 July with the Chandra X-Ray Observatory. The inferred 0.5-10 keV unabsorbed flux is in the range (2.5-5.0) x 10(-15) erg s(-1) cm. Notwithstanding large distance uncertainties, the measured luminosity is comparable to that of the faintest detected black hole X-ray binaries, all having orbital periods close to the expected bifurcation period between j-and n-driven low-mass X-ray binaries. This suggests that a few erg s(-1) might be a limiting luminosity value for quiescent black holes.