Prominent Polarized Flares of the Blazars AO 0235164 and PKS 1510089

We report on multi-band photometric and polarimetric observations of the blazars AO 0235$+$164 and PKS 1510$-$089. These two blazars were active in 2008 and 2009, respectively. In these active states, prominent short flares were observed in both objects, having amplitudes of >1mag within 10d. The V-J color became bluer when the objects were brighter in these flares. On the other hand, the color of PKS 1510$-$089 exhibited a trend that it became redder when it was brighter, except for its prominent flare. This redder-when-brighter trend can be explained by the strong contribution of thermal emission from an accretion disk. The polarization degree increased at the flares, and reached >25% at the maxima. We compared these flares in AO 0235$+$164 and PKS 1510$-$089 with other short flares that were detected by our monitoring of 41 blazars. Those two flares had one of the largest variation amplitudes in both flux and polarization degree. Furthermore, we found a significant positive correlation between the amplitudes of the flux and the polarization degree in short flares. It indicates that the short flares originate from the region where the magnetic field is aligned.