  Recently, Narayan, Garcia and McClintock showed that there is a difference in
the quiescent luminosities of black hole and neutron star x-ray nova: when the
quiescent, Eddington scaled luminosities are compared, every black hole x-ray
nova (BHXN) is fainter than every the neutron star x-ray nova (NSXN). To this
earlier work we add three more BHXN, GRO J1655-40, GRO J0422+32, and 4U1543-47.
This increases the significance of the difference between the quiescent
luminosities to the >99% level. Given the reasonable assumption that the
(Eddington scaled) mass transfer swings in BHXN and NSXN are similar, this
difference provides direct evidence for the existence of event horizons in the
BHXN: they have larger luminosity swings because the quiescent mass transfer
energy is being hidden behind the event horizon.
