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

TL;DR

This study analyzes long-term and intra-year microlensing variability in the gravitationally lensed quasar FBQ 0951+2635, finding evidence for long-timescale fluctuations rather than rapid, short-term events.

Contribution

It provides new multi-year R-band and i-band observations that distinguish between short and long-timescale microlensing variability in this quasar.

Findings

No evidence of short-timescale microlensing in 2004 and 2007.

Flux ratio shows a long-term fluctuation with a bump in 2003-2004.

Results favor long-timescale variability over rapid flares.

Abstract

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