Radio and optical intra-day variability observations of five blazars
  We carried out a pilot campaign of radio and optical band intra-day
variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287,
B0925+504, and BL Lacertae) on December 18--21, 2015 by using the radio
telescope in Effelsberg (Germany) and several optical telescopes in Asia,
Europe, and America. After calibration, the light curves from both 5 GHz radio
band and the optical R band were obtained, although the data were not smoothly
sampled over the sampling period of about four days. We tentatively analyse the
amplitudes and time scales of the variabilities, and any possible periodicity.
The blazars vary significantly in the radio (except 3C66A and BL Lacertae with
only marginal variations) and optical bands on intra- and inter-day time
scales, and the source B0925+504 exhibits a strong quasi-periodic radio
variability. No significant correlation between the radio- and optical-band
variability appears in the five sources, which we attribute to the radio IDV
being dominated by interstellar scintillation whereas the optical variability
comes from the source itself. However, the radio- and optical-band variations
appear to be weakly correlated in some sources and should be investigated based
on well-sampled data from future observations.
