Letter to the Editor

Microlensing variability in time-delay quasars

¹ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark e-mail: danutas@astro.ku.dk
² Nordic Optical Telescope (NOT), Apartado 474, 38700 Santa Cruz de La Palma, Canary Islands, Spain
³ Norwegian Meteorological Institute, PO Box 43, Blindern, 031 3 Oslo, Norway

Received: 26 April 2006
Accepted: 15 May 2006

Abstract

We have searched for microlensing variability in the light curves of five gravitationally lensed quasars with well-determined time delays: SBS 1520+530, FBQ 0951+2635, RX J0911+0551, B1600+434 and HE 2149-2745. By comparing the light curve of the leading image with a suitably time offset light curve of a trailing image we find that two (SBS 1520+530 and FBQ 0951+2635) out of the five quasars have significant long-term (~years) and short-term (~100 days) brightness variations that may be attributed to microlensing. The short-term variations may be due to nanolenses , relativistic hot or cold spots in the quasar accretion disks, or coherent microlensing at large optical depth.