Fk. Baganoff et Ma. Malkan, GRAVITATIONAL MICROLENSING IS NOT REQUIRED TO EXPLAIN QUASAR VARIABILITY, The Astrophysical journal, 444(1), 1995, pp. 13-15
In a recent Letter to Nature, Hawkins presents a statistical analysis
of about 300 quasar light curves which appears to indicate that high-r
edshift quasar variability is the result of microlensing by intervenin
g compact substellar-mass objects (i.e., brown dwarfs). This contradic
ts the general belief that high-redshift quasar variability is predomi
nantly intrinsic. Furthermore, Hawkins states that the density of lens
ing objects required to produce the observed light curves must be at l
east 0.1 of the critical density needed to close the universe. Thus a
prominent constituent of the total mass of the universe would be in th
e form of brown dwarf-sized baryonic dark matter, rather than the more
exotic particles being proposed by theoretical particle physicists to
explain the ''dark matter'' problem. In this Letter, we describe how
two well-known effects can be combined to account for Hawkins's observ
ations within the context of intrinsic variability models. We show tha
t observed timescales of intrinsic quasar variability at a fixed obser
ved wavelength should not be expected to correlate linearly with (1 z), contrary to common perception. We conclude that the evidence at th
is time does not require the gravitational microlensing hypothesis to
explain high-redshift quasar variability.