  The Advanced LIGO and Virgo experiments are poised to detect gravitational
waves (GWs) directly for the first time this decade. The ultimate prize will be
joint observation of a compact binary merger in both gravitational and
electromagnetic channels. However, GW sky locations that are uncertain by
hundreds of square degrees will pose a challenge. I describe a real-time
detection pipeline and a rapid Bayesian parameter estimation code that will
make it possible to search promptly for optical counterparts in Advanced LIGO.
Having analyzed a comprehensive population of simulated GW sources, we describe
the sky localization accuracy that the GW detector network will achieve as each
detector comes online and progresses toward design sensitivity. Next, in
preparation for the optical search with the intermediate Palomar Transient
Factory (iPTF), we have developed a unique capability to detect optical
afterglows of gamma-ray bursts (GRBs) detected by the Fermi Gamma-ray Burst
Monitor (GBM). Its comparable error regions offer a close parallel to the
Advanced LIGO problem, but Fermi's unique access to MeV-GeV photons and its
near all-sky coverage may allow us to look at optical afterglows in a
relatively unexplored part of the GRB parameter space. We present the discovery
and broadband follow-up observations of eight GBM-iPTF afterglows. Two of the
bursts are at low redshift, are sub-luminous with respect to "standard"
cosmological bursts, and have spectroscopically confirmed broad-line type Ic
supernovae. These two bursts are possibly consistent with mildly relativistic
shocks breaking out from the progenitor envelopes rather than the standard
mechanism of internal shocks within an ultra-relativistic jet. On a technical
level, the GBM-iPTF effort is a prototype for locating and observing optical
counterparts of GW events in Advanced LIGO with the Zwicky Transient Facility.
