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The quasar 3C 454.3 is a blazar known for its rapid and violent outbursts seen across the electromagnetic spectrum. Using gamma-ray, X-ray, multi-band optical, and very long baseline interferometric data we investigate the nature of two such events that occurred in 2013 and 2014 accompanied by strong variations in optical polarization, including a 230 degree electric vector position angle (EVPA) rotation. Our results suggest that a single disturbance was responsible for both flaring events. We interpret the disturbance as a shock propagating down the jet. Under this interpretation the 2013-flare originated most likely due to changes in the viewing angle caused by perhaps a bent or helical trajectory of the shock upstream of the radio core. The 2014-flare and optical polarization behavior are the result of the shock exiting the 43 GHz radio core, suggesting that shock crossings are one of the possible mechanisms for EVPA rotations., Comment: 14 pages, 10 figures, 2 Tables, accepted for publication in The Astrophysical Journal

We analyze the linear polarization of the relativistic jet in BL Lacertae object OJ 287 as revealed by multi-epoch Very Long Baseline Array images at 43 GHz and monitoring observations at optical bands. The electric-vector position angle of the optical polarization matches that at 43 GHz at locations that are often in the compact millimeter-wave >core> or, at other epochs, coincident with a bright, quasi-stationary emission feature ∼0.2 mas (∼0.9 pc projected on the sky) downstream from the core. This implies that electrons with high enough energies to emit optical synchrotron and γ-ray inverse Compton radiation are accelerated both in the core and at the downstream feature, the latter of which lies ≥10 pc from the central engine. The polarization vector in the stationary feature is nearly parallel to the jet axis, as expected for a conical standing shock capable of accelerating electrons to GeV energies.© 2018. The American Astronomical Society. All rights reserved.., The authors thank Dr. Ioannis Myserlis for a critical review of a draft of this manuscript. The authors acknowledge financial support by MEXT/JSPS Grant-in-Aid for Scientific Research on Innovative Areas (No. 25120007). M.S. was supported during this study by a JSPS Postdoctoral Fellowship for Research Abroad. The research at Boston University was supported in part by National Science Foundation grant AST-1615796 and NASA Fermi Guest Investigator Program grants NNX14AQ58G and 80NSSC17K0649. The St. Petersburg University team acknowledges support from Russian Science Foundation grant 17-12-01029. I.A. acknowledges support by a Ramon y Cajal grant of the Ministerio de Economia y Competitividad (MINECO) of Spain. The research at the IAA-CSIC was supported in part by the MINECO through grants AYA2016-80889-P, AYA2013-40825-P, and AYA2010-14844; and by the regional government of Andalucia through grant P09-FQM-4784. Calar Alto Observatory is jointly operated by the Max-Planck-Institut fur Astronomie and the IAA-CSIC. The VLBA is an instrument of the Long Baseline Observatory (LBO). The LBO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Data from the Steward Observatory spectro-polarimetric monitoring project were used. This program was supported by Fermi Guest Investigator grants NNX08AW56G, NNX09AU10G, NNX12AO93G, and NNX15AU81G.

We present results from monitoring the multi-waveband flux, linear polarization, and parsec-scale structure of the quasar PKS 1510-089, concentrating on eight major gamma-ray flares that occurred during the interval 2009.0-2009.5. The gamma-ray peaks were essentially simultaneous with maxima at optical wavelengths, although the flux ratio of the two wavebands varied by an order of magnitude. The optical polarization vector rotated by 720 degrees during a 5-day period encompassing six of these flares. This culminated in a very bright, roughly 1 day, optical and gamma-ray flare as a bright knot of emission passed through the highest-intensity, stationary feature (the "core") seen in 43 GHz Very Long Baseline Array images. The knot continued to propagate down the jet at an apparent speed of 22c and emit strongly at gamma-ray energies as a months-long X-ray/radio outburst intensified. We interpret these events as the result of the knot following a spiral path through a mainly toroidal magnetic field pattern in the acceleration and collimation zone of the jet, after which it passes through a standing shock in the 43 GHz core and then continues downstream. In this picture, the rapid gamma-ray flares result from scattering of infrared seed photons from a relatively slow sheath of the jet as well as from optical synchrotron radiation in the faster spine. The 2006-2009.7 radio and X-ray flux variations are correlated at very high significance; we conclude that the X-rays are mainly from inverse Compton scattering of infrared seed photons by 20-40 MeV electrons., Comment: 10 pages of text + 5 figures, to be published in Astrophysical Journal Letters in 2010

We analyze the multifrequency behavior of the quasar 3C 454.3 during three prominent \gamma-ray outbursts: 2009 Autumn, 2010 Spring, and 2010 Autumn. The data reveal a repeating pattern, including a triple flare structure, in the properties of each \gamma-ray outburst, which implies similar mechanism(s) and location for all three events. The multi-frequency behavior indicates that the lower frequency events are co-spatial with the \gamma-ray outbursts, although the \gamma-ray emission varies on the shortest timescales. We determine that the variability from UV to IR wavelengths during an outburst results from a single synchrotron component whose properties do not change significantly over the different outbursts. Despite a general increase in the degree of optical linear polarization during an outburst, the polarization drops significantly at the peak of the \gamma-ray event, which suggests that both shocks and turbulent processes are involved. We detect two disturbances (knots) with superluminal apparent speeds in the parsec-scale jet associated with the outbursts in 2009 Autumn and 2010 Autumn. The kinematic properties of the knots can explain the difference in amplitudes of the \gamma-ray events, while their millimeter-wave polarization is related to the optical polarization during the outbursts. We interpret the multi-frequency behavior within models involving either a system of standing conical shocks or magnetic reconnection events located in the parsec-scale millimeter-wave core of the jet. We argue that \gamma-ray outbursts with variability timescales as short as ~ 3 hr can occur on parsec scales if flares take place in localized regions such as turbulent cells., Comment: 80 pages, 10 Tables, 31 figures, accepted for publication in ApJ