  Kawahara and collaborators analyzed the transits of the candidate
disintegrating Mercury-mass planet KIC 12557548b and suggested that the transit
depths were correlated with the phase of the stellar rotation. We analyze the
transit depths of KIC 12557548b and confirm that there is indeed a robust,
statistically significant signal in the transit depths at the rotation period
of the spotted host star. This signal is more prominent in the first-half of
the Kepler data, and is not due to leakage of the rotating spot signal into our
measurement of the transit depths, or due to unocculted starspots. We
investigate the suggestion that this signal could be due to an active region on
the star, emitting enhanced ultraviolet or X-ray radiation leading to an
increased mass loss rate of the planet; we confirm that such a scenario could
cause both modulation of the transit depths of KIC 12557548b, and small enough
transit-timing variations that they might not be detected in the Kepler data.
Our preferred explanation for the fact that the transit depths of KIC 12557548b
are modulated with the stellar rotation phase is that the candidate transiting
planet is occulting starspots on this highly spotted star; such a scenario
could cause transit depth variations as large as have been observed, and cause
transit-timing variations small enough that they are arguably consistent with
the Kepler data.
