  TWA 3A is the most recent addition to a small group of young binary systems
that both actively accrete from a circumbinary disk and have spectroscopic
orbital solutions. As such, it provides a unique opportunity to test binary
accretion theory in a well-constrained setting. To examine TWA 3A's
time-variable accretion behavior, we have conducted a two-year, optical
photometric monitoring campaign, obtaining dense orbital phase coverage (~20
observations per orbit) for ~15 orbital periods. From U-band measurements we
derive the time-dependent binary mass accretion rate, finding bursts of
accretion near each periastron passage. On average, these enhanced accretion
events evolve over orbital phases 0.85 to 1.05, reaching their peak at
periastron. The specific accretion rate increases above the quiescent value by
a factor of ~4 on average but the peak can be as high as an order of magnitude
in a given orbit. The phase dependence and amplitude of TWA 3A accretion is in
good agreement with numerical simulations of binary accretion with similar
orbital parameters. In these simulations, periastron accretion bursts are
fueled by periodic streams of material from the circumbinary disk that are
driven by the binary orbit. We find that TWA 3A's average accretion behavior is
remarkably similar to DQ Tau, another T Tauri binary with similar orbital
parameters, but with significantly less variability from orbit to orbit. This
is only the second clear case of orbital-phase-dependent accretion in a T Tauri
binary.
