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In an optical monitoring program to characterize the variability propertiesof blazar, we observed 10 sources from the Roma-BZCAT catalogue for 26 nightsin V and R bands during October 2014 to June 2015 with two telescopes locatedin India. The sample includes mainly newly discovered BL Lacs where theredshift of some sources are not known yet. We present the results of flux andcolor variations of the sample on intraday and short time scales obtained byusing the power-enhanced F-test and the nested-ANOVA tests, along with theirspectral behavior. We find significant intraday variability in the single FSRQin our sample, having an amplitude of variation ~12%. Although a few of BL Lacsshowed probable variation in some nights, none of them passes the variabilitytests at 99.9% significance level. We find that 78% of the sample showedsignificant negative colour--magnitude correlations i.e., aredder-when-brighter spectral evolution. Those which do not show strong orclear chromatism, predominantly exhibit a redder-when-brighter trends. Unlikeon hourly timescales, the high synchrotron peaked (HSP) blazars in the sample(BZGJ0656+4237, BZGJ0152+0147 and BZBJ1728+5013) show strong flux variation ondays to months timescales, where again we detect a decreasing trend of thespectral slope with brightness. We observe a global steepening of the opticalspectrum with increasing flux on intranight timescale for the entire blazarsample. Non-variability in the BL Lacs in our sample could be resulted bydistinct contribution from the disk as well as from other components in thestudied energy range.

Optical variability of a newly discovered blazar sample from the BZCAT Catalog