Enhanced probability of intensity outbursts via superluminal microlensing of quasars

Abstract

The apparent faster-than-light motion of the emission knots associated with relativistic jets of quasars implies that relative to the stars of any foreground galaxy, their motion could easily be superluminal and thus a few orders-of-magnitude faster than the stellar velocities. The resulting "superluminal microlensing" of the emission knots would not only impress an ultra-rapid flux variability on even intrinsically non-varying jets, as proposed by us previously, but the probability of seeing microlensing events would itself be markedly enhanced, particularly when the intrinsic optical depth of the galaxy for microlensing is modest (~ 0.1). The probabilities are quantitatively estimated for the simple but plausible case of the dark galactic halos being made of low mass stars, or Jupiter-like bodies. For a given duration of observation, the likelihood of microlensing events could widely differ depending on whether the emission from the lensed source is dominated by a relativistic jet, or by a stationary component.