The importance of discovering a 3:2 twin-peak QPO in a ULX or how to solve the puzzle of intermediate mass black holes

摘要

Recently, twin-peak QPOs have been observed in a 3:2 ratio for three Galacticblack-hole microquasars with frequencies that have been shown to scale as 1/M,as expected for general relativisitic motion near a black hole. It may bepossible to extend this result to distinguish between the following twodisparate models that have been proposed for the puzzling ultraluminous X-raysources (ULXs): (1) an intermediate-mass black hole M ~1000 solar mass)radiating very near the Eddington limit and (2) a conventional black hole (M ~10 solar mass) accreting at a highly super-Eddington rate with its emissionbeamed along the rotation axis. We suggest that it may be possible todistinguish between these models by detecting the counterpart of a Galactictwin-peak QPO in a ULX: the expected frequency for the intermediate-mass blackhole model is only about 1 Hz, whereas, for the conventional black hole modelthe expected frequency would be the ~100 Hz value observed for the Galacticmicroquasars.