SIMBAD references

We investigate the effects of observatory location on the probability of discovering optical/infrared (OIR) counterparts of gravitational wave sources. We show that, for the LIGO-Virgo network, the odds of discovering OIR counterparts show some latitude dependence. A stronger effect is seen to arise from the timing of LIGO-Virgo observing runs during the year, with northern OIR observatories having a better chance of finding the counterparts in northern winters. Assuming identical technical capabilities, the tentative mid-2017 three-detector network observing run favors southern OIR observatories for the discovery of electromagnetic counterparts.