We report on BeppoSAX observations of five transient black hole candidates during their quiescent phase .
We confirm these sources are X–ray faint , improving on and complementing existing upper limits .
We derive 1–10 keV upper limits for GRO J0422+32 , GRS 1009–45 , 4U 1630–47 and XTE J1748–288 , which range from 2 \times 10 ^ { 32 } erg s ^ { -1 } to 5 \times 10 ^ { 34 } erg s ^ { -1 } .
We positively detect GS 2023+338 .
Its X–ray spectrum can be fit by a power law ( photon index \Gamma = 1.9 ) or a thermal bremsstrahlung ( with k T _ { br } = 7 keV ) , converting in both cases to a 1–10 keV unabsorbed luminosity of \sim 10 ^ { 33 } erg s ^ { -1 } .
These values are comparable to the ones derived during an ASCA observation in 1994 , indicating that the source remains stable over a \sim 5 yr baseline .