Final answer:
Observations of accretion disks around white dwarfs should primarily be conducted in the X-ray band for high-energy processes, the visible spectrum for large-scale disk structures, and the radio spectrum for extended, cooler parts of the disk.
Step-by-step explanation:
To determine in what wavebands to observe the accretion disk around a white dwarf, one needs to consider the energy and temperature of the accretion disk, as well as the light travel time. Accretion disks around white dwarfs often emit significant energy in the X-ray band, as this high-energy radiation indicates the presence of very hot material and high-energy processes occurring near the white dwarf. From the information provided, X-ray observations have detected hot white dwarfs with X-ray glowing accretion disks. This suggests that observing in the X-ray band is particularly effective for studying the inner regions of the accretion disk close to the white dwarf.
Moreover, the visible light variation timescales observed in quasars can limit the size of the regions studied. Observations in the visible spectrum are informative for detecting changes over time, suggesting that this could be useful for studying larger structures of an accretion disk which may emit visible light as the disk material heats up. However, observations in the radio spectrum, particularly at 21-cm wavelength, can penetrate through dust and may also be beneficial for detecting cooler, more extended parts of the disk.
In summary, to observe an accretion disk around a white dwarf, one should primarily utilize the X-ray spectrum for high-energy characteristics, the visible spectrum for large disk structures, and potentially the radio spectrum for extended, cooler regions of the disk.