  Gravitational waves carry unique information about high-energy astrophysical
events such as the inspiral and merger of neutron stars and black holes, core
collapse in massive stars, and other sources. Large gravitational wave (GW)
detectors utilizing exquisitely sensitive laser interferometry--namely, LIGO in
the United States and GEO 600 and Virgo in Europe--have been successfully
operated in recent years and are currently being upgraded to greatly improve
their sensitivities. Many signals are expected to be detected in the coming
decade. Simultaneous observing with the network of GW detectors enables us to
identify and localize event candidates on the sky with modest precision,
opening up the possibility of capturing optical transients or other
electromagnetic counterparts to confirm an event and obtain complementary
information about it. We developed and implemented the first complete
low-latency GW data analysis and alert system in 2009-10 and used it to send
alerts to several observing partners; the system design and some lessons
learned are briefly described. We discuss several operational considerations
and design choices for improving this scientific capability for future
observations.
