  Based on more than four weeks of continuous high cadence photometric
monitoring of several hundred members of the young cluster NGC 2264 with two
space telescopes, NASA's Spitzer and the CNES CoRoT (Convection, Rotation, and
planetary Transits), we provide high quality, multi-wavelength light curves for
young stellar objects (YSOs) whose optical variability is dominated by short
duration flux bursts, which we infer are due to enhanced mass accretion rates.
These light curves show many brief -- several hour to one day -- brightenings
at optical and near-infrared (IR) wavelengths with amplitudes generally in the
range 5-50% of the quiescent value. Typically, a dozen or more of these bursts
occur in a thirty day period. We demonstrate that stars exhibiting this type of
variability have large ultraviolet (UV) excesses and dominate the portion of
the u-g vs. g-r color-color diagram with the largest UV excesses. These stars
also have large Halpha equivalent widths, and either centrally peaked, lumpy
Halpha emission profiles or profiles with blue-shifted absorption dips
associated with disk or stellar winds. Light curves of this type have been
predicted for stars whose accretion is dominated by Rayleigh-Taylor
instabilities at the boundary between their magnetosphere and inner
circumstellar disk, or where magneto-rotational instabilities modulate the
accretion rate from the inner disk. Amongst the stars with the largest UV
excesses or largest Halpha equivalent widths, light curves with this type of
variability greatly outnumber light curves with relatively smooth sinusoidal
variations associated with long-lived hot spots. We provide quantitative
statistics for the average duration and strength of the accretion bursts and
for the fraction of the accretion luminosity associated with these bursts.
