The 2016 June optical and gamma-ray outburst and optical microvariability of the blazar 3C 454.3

Abstract

The quasar 3C 454.3 underwent a uniquely structured multifrequency outburst in 2016 June. The blazar was observed in the optical R-band by several ground-based telescopes in photometric and polarimetric modes, at γ-ray frequencies by the Fermi Large Area Telescope, and at 43 GHz with the Very Long Baseline Array. The maximum flux density was observed on 2016 June 24 at both optical and γ-ray frequencies, reaching {S}_{\mathrm{opt}}^{\max }=18.91\pm 0.08 mJy and {S}_{\gamma }^{\max }=22.20\pm 0.18\times {10}^{-6} ph cm−2 s−1, respectively. The 2016 June outburst possessed a precipitous decay at both γ-ray and optical frequencies, with the source decreasing in flux density by a factor of 4 over a 24 hr period in the R-band. Intraday variability was observed throughout the outburst, with flux density changes between 1 and 5 mJy over the course of a night. The precipitous decay featured statistically significant quasiperiodic microvariability oscillations with an amplitude of ~2%–3% about the mean trend and a characteristic period of 36 minutes. The optical degree of polarization jumped from ~3% to nearly 20% during the outburst, while the position angle varied by ~120°. A knot was ejected from the 43 GHz core on 2016 February 25, moving at an apparent speed {v}_{\mathrm{app}}=20.3c\pm 0.8c. From the observed minimum timescale of variability {\tau }_{\mathrm{opt}}^{\min }\approx 2\,\mathrm{hr} and derived Doppler factor δ = 22.6, we find the size of the emission region r lesssim 2.6 × 1015 cm. If the quasiperiodic microvariability oscillations are caused by periodic variations of the Doppler factor of emission from a turbulent vortex, we derive the rotational speed of the vortex to be ~0.2c.