Limits on the Transverse Velocity of the Lensing Galaxy in Q2237+0305 from the Lack of Strong Microlensing Variability

Rodrigo Gil-Merino, Joachim Wambsganss, Luis J. Goicoechea, Geraint F. Lewis

Published 2004-11-09Version 1

We present a method for the determination of upper limits on the transverse velocity of the lensing galaxy in the quadruple quasar system Q2237+0305, based on the lack of strong microlensing signatures in the quasar lightcurves. The limits we derive here are based on four months of high quality monitoring data, by comparing the low amplitudes of the lightcurves of the four components with extensive numerical simulations. We make use of the absence of strong variability of the components (especially components B and D) to infer that a "flat" time interval of such a length is only compatible with an effective transverse velocity of the lensing galaxy of v_bulk <=630 km/s for typical microlenses masses of M_microlens=0.1 M_solar (or v_bulk <=2160 km/s for M_microlens=1.0 M_solar) at the 90% confidence level. This method may be applicable in the future to other systems.