Spectrophotometric variability of quasars caused by lensing of diffuse massive substructure: Consequences on flux anomaly and precise astrometric measurements

Abstract

We investigate the spectrophotometric variability of quasars due to lensing of small mass substructure (from several tens to several hundreds solar masses). The aim of this paper is to explore the milli/microlensing influence on the flux anomaly observed between images of a lensed quasar in different spectral bands and the possible influence of small mass structure lensing of non-macrolensed quasars. We find that spectrophotometric variability may also be caused by lensing of small mass diffuse structure and can produce the flux anomaly, which is sometimes seen in different images of a lensed quasar.Additionally, we found that the lensing by small mass diffuse structure may produce significant changes in the photocentre position of a quasar, and sometimes can split or deviate images of one source that can be detected as separate from the scale from 0.1 to several milliarcseconds. This can be measured with Gaia-like space astrometric missions.We point out a special case where a low redshifted deflector (zd̃0.01) is lensing a high redshifted source for which the variability in the flux and photocentre (several milliarcseconds) may be detected on a relatively short time-scale. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.