1998A&A...333..583R

The six known low mass black hole binaries discovered as X-ray/Optical novae represent a relatively uniform source class. It is shown that the recurrence time for outbursts from these sources can be understood in the disk instability picture if magnetic braking is not active in the short period systems. An extrapolation from the discovery surveys gives an estimate of ∼1700 such systems in the Galaxy as a whole. BATSE sky monitor observations should produce new candidate black hole transients at a rate of ∼2/y. The population estimates also suggest that >13 optical outbursts of black hole binaries prior to 1975 should have been recorded in classical nova catalogues. Some strategies for discovery of more black hole binaries are discussed.