2019ApJ...880..155L

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 ΔI ≃ 0.06 ± 0.01 mag in a duration of 0.54 hr for S5 0716+714. A flare on 2011 May 10 shows ΔR ≃ 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 ΔR ≃ 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_* <= 10^8.91 M_☉ and M_* <= 10^9.02 M_☉ 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.