Search for Intra-day Optical Variability in γ-Ray-loud Blazars S5 0716+714 and 3C 273

We present the photometric observations of blazars S5 0716+714 and 3C 273 with high temporal resolution (30-60 s) in the I or R bands. The observations were performed with a 1.02 m optical telescope from 2007 March 7 to 2012 May 16. The F-test, one-way analysis of variance (ANOVA) test, and z-transformed discrete correlation function (ZDCF) cross-correlation zero lag test are used to search for intra-day variability (IDV). Four and five reliable IDVs survive three tests for S5 0716+714 and 3C 273, respectively. IDVs are found for S5 0716+714 and 3C 273. A flare on 2008 May 8 has Delta I approximate to 0.06 +/- 0.01 mag in a duration of 0.54 hr for S5 0716+714. A flare on 2011 May 10 shows Delta R approximate to 0.05 +/- 0.01 mag in a duration of 0.40 hr for 3C 273. Sharp dips appear on 2011 May 9 for 3C 273 and show Delta R approximate to 0.05 +/- 0.01 mag. Under the assumptions that the IDV is tightly connected to black hole mass, M., and that the flare durations are representative of the minimum characteristic timescales, we can estimate upper bounds to M.. In the case of the Kerr black holes, M. less than or similar to 10(8.91) M-circle dot and M. less than or similar to 10(9.02) M-circle dot are given for S5 0716+714 and 3C 273, respectively. These mass measurements are consistent with those measurements reported in the literature. Also, we discuss the origins of optical variations found in this work.