Microlensing variability in FBQ 0951+2635: short-timescale events or a long-timescale fluctuation?

摘要

We present and analyse new R-band frames of the gravitationally lensed doublequasar FBQ 0951+2635. These images were obtained with the 1.5m AZT-22 Telescopeat Maidanak (Uzbekistan) in the 2001-2006 period. Previous results in the Rband (1999-2001 period) and the new data allow us to discuss the dominant kindof microlensing variability in FBQ 0951+2635. The time evolution of the fluxratio A/B does not favour the continuous production of short-timescale (months)flares in the faintest quasar component B (crossing the central region of thelensing galaxy). Instead of a rapid variability scenario, the observations areconsistent with the existence of a long-timescale fluctuation. The flux ratioshows a bump in the 2003-2004 period and a quasi-flat trend in more recentepochs. Apart from the global behaviour of A/B, we study the intra-yearvariability over the first semester of 2004, which is reasonably well sampled.Short-timescale microlensing is not detected in that period. Additional data inthe i band (from new i-band images taken in 2007 with the 2m Liverpool RoboticTelescope at La Palma, Canary Islands) also indicate the absence ofshort-timescale events in 2007.