  Context. The bipolar outflows associated with low-mass protostars create
cavities in the infalling envelope. These cavities are illuminated by the
central protostar and inner disk, creating a bipolar scattered light nebula at
near-infrared and mid-infrared wavelengths. The variability of the scattered
light nebula in both total intensity and intensity as a function of position in
the scattered light nebula can provide important insights into the structure of
the inner disk that cannot be spatially resolved. Aims. We aim to determine the
likelihood that a warped inner disk is the origin of the surface brightness
variability in the bipolar scattered light nebula associated with L1527 IRS.
Methods. We present results from near-IR imaging conducted over the course of
seven years, with periods of monthly cadence monitoring. We used Monte Carlo
radiative transfer models to interpret the observations. Results. We find a
time varying, asymmetrical brightness in the scattered light nebulae within the
outflow cavities of the protostar. Starting in 2007, the surface brightnesses
of the eastern and western outflow cavities were roughly symmetric. Then, in
2009, the surface brightnesses of the cavities were found to be asymmetric,
with a substantial increase in surface brightness and a larger increase in the
eastern outflow cavity. More regular monitoring was conducted from 2011 to
2014, revealing a rotating pattern of surface brightness variability in
addition to a slow change of the eastern and western outflow cavities toward
symmetry, but still not as symmetric as observed in 2007. We find that an inner
disk warp is a feasible mechanism to produce the rotating pattern of surface
brightness variability.
