Abstract
In this paper we have used calibrated data from the Virgo second (Aasi et al. 2012CQGra..29o5002A) and fourth science runs (VSR2 and VSR4) and the LIGO sixth science run (S6). Virgo's third science run (VSR3) was relatively insensitive in comparison with VSR4 and has not been included in this analysis. This was partially because Virgo introduced monolithic mirror suspensions prior to VSR4 which improved sensitivity in the low-frequency range. During S6, the two LIGO 4 km detectors at Hanford, Washington (LHO/H1), and Livingston, Louisiana (LLO/L1), were running in an enhanced configuration (Adhikari et al. 2006, Enhanced LIGO, Tech. Rep. LIGO-T060156-v01, California Institute of Technology, Massachusetts Institute of Technology, https://dcc.ligo.org/LIGO-T060156-v1/public) over that from the previous S5 run (Abbott et al. 2009RPPh...72g6901A).
