A BeppoSAX view of transient black hole candidates in quiescence

We report BeppoSAX observations of five transient black hole candidates dur ing their quiescent phase. We confirm that these sources are X-ray faint, i mproving on and complementing existing upper limits. We derive 1-10 keV upp er limits for GRO J0422+32, GRS 1009-45, 4U 1630-47 and XTE J1748-288, whic h range from 2 x 10(32) erg s(-1) to 5 x 10(34) erg s(-1). We positively de tect GS 2023+338. Its X-ray spectrum can be fit by a power law (photon inde x Gamma = 1.9) or a thermal bremsstrahlung (with k T-br = 7 keV), convertin g in both cases to a 1-10 keV unabsorbed luminosity of similar to 10(33) er g s(-1). These values are comparable to the ones derived during an ASCA obs ervation in 1994, indicating that the source remains stable over a similar to5 yr baseline.