Multiwaveband quasi-periodic oscillation in the blazar 3C 454.3

Abstract

We report the detection (>4σ) of a Quasi-Periodic Oscillation (QPO) in the γ-ray light curve of 3C 454.3 along with a simultaneous marginal QPO detection (>2.4σ) in the optical light curves. Periodic flux modulations were detected in both of these wavebands with a dominant period of ∼47 days. The γ-ray QPO lasted for over 450 days (from MJD 56800 to 57250) resulting in over nine observed cycles which is among the highest number of periods ever detected in a blazar light curve. The optical light curve was not well sampled for almost half of the γ-ray QPO span due to the daytime transit of the source, which could explain the lower significance of the optical QPO. Autoregressive Integrated Moving Average (ARIMA) modelling of the light curve revealed a significant, exponentially decaying, trend in the light curve during the QPO, along with the 47 days periodicity. We explore several physical models to explain the origin of this transient quasi-periodic modulation and the overall trend in the observed flux with a month-like period. These scenarios include a binary black hole system, a hotspot orbiting close to the innermost stable circular orbit of the supermassive black hole, and precessing jets. We conclude that the most likely scenario involves a region of enhanced emission moving helically inside a curved jet. The helical motion gives rise to the QPO and the curvature (∼0.05○ pc−1) of the jet is responsible for the observed trend in the light curve.

Transient Quasi-Periodic Oscillations at $γ$-rays in the TeV Blazar PKS 1510-089

“…Although the nature of blazar variability is mostly non-linear, stochastic and aperiodic (Kushwaha et al 2017), many studies have claimed detections of strong quasi-periodic oscillations (QPO) in blazar lightcurves of different electromagnetic wavebands. In accordance to the variability timescales, the reported QPOs range from a few tens of minutes to hours to days and even years of timescales ★ E-mail: abhradeep.roy@tifr.res.in (Raiteri et al 2001;Liu et al 2006;Gupta et al 2009;Lachowicz et al 2009;King et al 2013;Gupta 2014Gupta , 2018Gupta et al 2019;Ackermann et al 2015;Zhou et al 2018;Bhatta 2019;Sarkar et al 2020a;Sarkar et al 2020b, and references therein). However, most of the QPOs claimed in older studies are marginal detections in that they lasted for only a 2-4 cycles, while their significances were overestimated (Gupta 2014).…”

“…We can also attempt to attribute both the 3.6-day and 92-day QPO of PKS 1510-089 to a very reasonable model that involves a plasma blob moving helically down the jet (Mohan & Mangalam 2015;Sobacchi et al 2016;Sarkar et al 2020a). For the simplest leptonic one-zone model (where the bulk of the synchrotron and inverse-Compton emission comes from a single region), such a plasma blob contains higher particle and magnetic energy densities and is responsible for occasional enhanced emission from blazars.…”

“…It is evident from Figure 3a and Figure 4a that both the QPOs in EP1 and EP2 have varying amplitudes. We note that Sarkar et al (2020a) used a curved jet scenario to model a transient QPO with varying amplitude in 3C 454.3. In this model, the angle between the jet axis and our line of sight (𝜓) becomes time-dependent (𝜓(𝑡)).…”

“…In recent studies (Kushwaha et al 2020b;Sarkar et al 2020a;Peñil et al 2020;Sarkar et al 2020b), the reported blazar QPOs generally have >3𝜎 significance and cross the REDFIT FAP level of 1%. In this case, the QPO spans only 18 days and the apparent periodicity is very fast (∼3.6 days) which should be the reason for low significance in the REDFIT output.…”

“…Continuous monitoring of blazars by Fermi-LAT in the last 12years has led to a few recent highly significant 𝛾-ray QPO detections in different blazars, including a ∼34.5-day transient QPO in PKS 2247-131 (Zhou et al 2018), a ∼71-day transient QPO in B2 1520+31 (Gupta et al 2019), a ∼47-day QPO in 3C 454.3 (Sarkar et al 2020a), a fast periodicity of ∼7.6 days in CTA 102 during an outburst (Sarkar et al 2020b), and a periodicity of ∼314 days in OJ 287 (Kushwaha et al 2020a). Although Covino et al (2019) did the periodogram analysis on the Fermi-LAT aperture photometry lightcurves of 10 blazars and claimed the absence of any global significant periodicity in 𝛾-rays, a more systematic approach to 𝛾-ray QPO detection by Peñil et al (2020), involving multiple independent techniques applied on about 2300 AGNs, revealed the presence of global periodicities of > 4𝜎 significance in 11 sources, along with 13 more sources with moderately significant (3-4𝜎) QPOs.…”