Abstract:
We present the results of our optical (VRI) observations of the TeV blazar PG 1553+113 over eight nights in 2016
April. We monitored the blazar quasi-simultaneously in V and R bands each night and examined the light curves
(LCs) for intraday flux and color variations using two of the most powerful tests: the power-enhanced F-test and
the nested ANOVA test. The source was found to be significantly (>99%) variable in both V and R bands only on
April 13, while clear variations only in R band LCs were seen on April 8 and 12. No temporal variation was seen in
the color during the observation period. We did not find any significant correlation between V − R color index and
R magnitude on any observing night. We found a mean optical spectral index of ∼0.83 ± 0.02 with a maximum
variation of 0.21 by fitting a power law (Fν ∝ ν− α
) in the optical (VRI) spectral energy distribution of PG 1553
+113. We briefly discuss the possible physical processes responsible for the observed flux and spectral variability.
