GW190521 and the GWTC-1 Events: Implication on the Black Hole Mass Function of Coalescing Binary Black Hole Systems

With the black hole mass function (BHMF; assuming an exponential cutoff at a mass of $sim 40,M_odot$) of coalescing binary black hole systems constructed with the events detected in the O1 run of the advanced LIGO/Virgo network, Liang et al.(2017) predicted that the birth of the lightest intermediate mass black holes (LIMBHs; with a final mass of $gtrsim 100,M_odot$) is very likely to be caught by the advanced LIGO/Virgo detectors in their O3 run. The O1 and O2 observation run data, however, strongly favor a cutoff of the BHMF much sharper than the exponential one. In this work we show that a power-law function followed by a sudden drop at $sim 40,M_odot$ by a factor of $sim $a few tens and then a new power-law component extending to $geq 100M_odot$ are consistent with the O1 and O2 observation run data. With this new BHMF, quite a few LIMBH events can be detected in the O3 observation run of advanced LIGO/Virgo. The first LIMBH born in GW190521, an event detected in the early stage of the O3 run of advanced LIGO/Virgo network, provides additional motivation for our hypothesis.