Radio (8.6 GHz) vs. X-ray luminosity (1–10 keV) diagram. Black squares indicate the positions of the 24 Galactic accreting binary black holes in the hard and quiescence states, as in Fig. 9 of Corbel et al. (2013; i.e., without the upper limits and neutron stars there present). The position of MWC 656 is indicated by two red squares for the two fluxes of 3.7 μJy and 14.2 μJy. The position of MWC 656 is rather close to the faintest accreting black hole systems known so far, A0620-00 (triangle, Gallo et al. 2006) and XTE J1118+480 (asterisk, Gallo et al. 2014).