tokens: 2013 ), ∼50 days in OJ 287 (Pihajoki et al. 2013 ); on an LTV timescale, QPOs of ∼12 yr, and ∼400 days in OJ 287 (Sillanpää et al. 1988 ; Valtonen et al. 2008 ; Bhatta et al. 2016 ), ∼3 yr in S5 0716+714 (Raiteri et al. 2003 ), ∼8 yr in BL Lacertae (Villata et al. 2004 ), ∼585 days in PKS B0048–097 (Kadler et al. 2006 ), ∼0.92 yr in PKS 1510–089 (Xie et al. 2008 ), 5–6 yr in AO 0235+164 (Raiteri et al. 2008 ), ∼420 days in 1ES 2321+419 (Rani et al. 2009 ), ∼6.3 yr in GB6 J1058+5628 (Nesci 2010 ), ∼10 and ∼6 yr in NRAO 530 (An et al. 2013 ), ∼315 days in PKS 2155–304 (Sandrinelli et al. 2014 ), 2.18 ± 0.08 yr in PG 1553+113 (Ackermann et al. 2015 ), and 5.2 yr in PG 1302–102 (Graham et al. 2015 ). However, the physical mechanism causing these possible periodicities is still unclear and requires further research . The physical mechanism of the quasi-periodic behavior in blazars is still in general controversial and not understood well. Several models have been proposed to interpret this behavior, although a few evidences for QPOs were detected. However, many in the scientific community are deeply skeptical of QPO claims where very few cycles are observed and/or one fails to account for random red noise variability (e.g., Tagliaferri et al. 1996 ; Benlloch et al. 2001 ; Vaughan 2005 ; Vaughan Uttley 2006 ; Espaillat et al. 2008 ; Gaur et al. 2010 ; Press 2013 ). Recently, Vaughan et al. ( 2016 ) reexamined the detection of periodic modulations of 5.2 yr in PG 1302−102 reported by Graham et al. ( 2015 ) and found that a simple stochastic process is preferred over a sinusoidal variation. They also emphasized that such a red noise stochastic process can occasionally mimic the sinusoid-like periodicity in a few-cycle light curve while the periodic candidate can be distinguished from a stochastic process by observing it for ∼5 cycles. Furthermore, we also note that many of the QPO claims mentioned above suffer from incomplete statistical analysis, e.g., periodicity claims in Sandrinelli et al. ( 2014 ), Ackermann et al. ( 2015 ), and Bhatta et al. ( 2016 ) only persist for a small number of cycles ; the baseline PSD in Ackermann et al. ( 2015 ) was difficult to measure and their light curve can be explained by a pure red noise process; Valtonen et al. ( 2008 ) and Wang Su ( 2016 ) failed to properly account for the random red noise variations; and Sandrinelli et al. ( 2014 ) seem to discuss only single-trial confidence limits instead of global significance limits. In our QPO analysis, the temporary sinusoid-like trends visually appearing for a few periods in 2012–2014 might cause a certain test of LSP and PDM analyses to spuriously indicate a QPO detection, and the stochastic red noise variability might dominate the total variance of the light curve and lead to the emergence of spurious peaks/dips appearing in the DACF. Although the significance of the candidate QPO is relatively low when accounting for the red noise processes, some discussions on
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