PROBING THE INNER JET OF THE QUASAR PKS 1510–089 WITH MULTI-WAVEBAND MONITORING DURING STRONG GAMMA-RAY ACTIVITY

Abstract

We present results from monitoring the multi-waveband flux, linear\npolarization, and parsec-scale structure of the quasar PKS 1510-089,\nconcentrating on eight major gamma-ray flares that occurred during the interval\n2009.0-2009.5. The gamma-ray peaks were essentially simultaneous with maxima at\noptical wavelengths, although the flux ratio of the two wavebands varied by an\norder of magnitude. The optical polarization vector rotated by 720 degrees\nduring a 5-day period encompassing six of these flares. This culminated in a\nvery bright, roughly 1 day, optical and gamma-ray flare as a bright knot of\nemission passed through the highest-intensity, stationary feature (the "core")\nseen in 43 GHz Very Long Baseline Array images. The knot continued to propagate\ndown the jet at an apparent speed of 22c and emit strongly at gamma-ray\nenergies as a months-long X-ray/radio outburst intensified. We interpret these\nevents as the result of the knot following a spiral path through a mainly\ntoroidal magnetic field pattern in the acceleration and collimation zone of the\njet, after which it passes through a standing shock in the 43 GHz core and then\ncontinues downstream. In this picture, the rapid gamma-ray flares result from\nscattering of infrared seed photons from a relatively slow sheath of the jet as\nwell as from optical synchrotron radiation in the faster spine. The 2006-2009.7\nradio and X-ray flux variations are correlated at very high significance; we\nconclude that the X-rays are mainly from inverse Compton scattering of infrared\nseed photons by 20-40 MeV electrons.\n