  We present multi-wavelength photometric monitoring of WD 1145+017, a white
dwarf exhibiting periodic dimming events interpreted to be the transits of
orbiting, disintegrating planetesimals. Our observations include the first set
of near-infrared light curves for the object, obtained on multiple nights over
the span of one month, and recorded multiple transit events with depths varying
between ~20 to 50 per cent. Simultaneous near-infrared and optical observations
of the deepest and longest duration transit event were obtained on two epochs
with the Anglo-Australian Telescope and three optical facilities, over the
wavelength range of 0.5 to 1.2 microns. These observations revealed no
measurable difference in transit depths for multiple photometric pass bands,
allowing us to place a 2 sigma lower limit of 0.8 microns on the grain size in
the putative transiting debris cloud. This conclusion is consistent with the
spectral energy distribution of the system, which can be fit with an optically
thin debris disc with minimum particle sizes of 10 +5/-3 microns.
