  Binary star-formation theory predicts that close binaries (a<100 AU) will
experience periodic pulsed accretion events as streams of material form at the
inner edge of a circumbinary disk, cross a dynamically cleared gap, and feed
circumstellar disks or accrete directly onto the stars. The archetype for the
pulsed-accretion theory is the eccentric, short-period, classical T Tauri
binary DQ Tau. Low-cadence (~daily) broadband photometry has shown brightening
events near most periastron passages, just as numerical simulations would
predict for an eccentric binary. Magnetic reconnection events (flares) during
the collision of stellar magnetospheres near periastron could, however, produce
the same periodic, broadband behavior when observed at a one-day cadence. To
reveal the dominate physical mechanism seen in DQ Tau's low-cadence
observations, we have obtained continuous, moderate-cadence, multi-band
photometry over 10 orbital periods, supplemented with 27 nights of
minute-cadence photometry centered on 4 separate periastron passages. While
both accretion and stellar flares are present, the dominant timescale and
morphology of brightening events are characteristic of accretion. On average,
the mass accretion rate increases by a factor of 5 near periastron, in good
agreement with recent models. Large variability is observed in the morphology
and amplitude of accretion events from orbit-to-orbit. We argue this is due to
the absence of stable circumstellar disks around each star, compounded by
inhomogeneities at the inner edge of the circumbinary disk and within the
accretion streams themselves. Quasi-periodic apastron accretion events are also
observed, which are not predicted by binary accretion theory.
