The microarcsecond structure of an AGN jet via interstellar scintillation

Abstract

We describe a new tool for studying the structure and physical characteristics of ultracompact AGN jets and their surroundings with microarcsecond precision. This tool is based on the frequency dependence of the light curves observed for intra-day variable radio sources, where the variability is caused by interstellar scintillation. We apply this method to PKS1257-326 to resolve the core-shift as a function of frequency on scales well below ~12 microarcseconds. We find that the frequency dependence of the position of the scintillating component is r \propto ν^{-0.1 \pm 0.24} (99% confidence interval) and the frequency dependence of the size of the scintillating component is d \propto ν^{-0.64 \pm 0.006}. Together, these results imply that the jet opening angle increases with distance along the jet: d \propto r^{n_d}$ with n_d > 1.8. We show that the flaring of the jet, and flat frequency dependence of the core position is broadly consistent with a model in which the jet is hydrostatically confined and traversing a steep pressure gradient in the confining medium with p \propto r^{-n_p} and n_p > 7. Such steep pressure gradients have previously been suggested based on VLBI studies of the frequency dependent core shifts in AGN.

accepted for publication in ApJ

References in corpus (4)

• The Structure of the M87 Jet: A Transition from Parabolic to Conical Streamlines
• Opacity in compact extragalactic radio sources and its effect on astrophysical and astrometric studies
• The Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey II: The First Four Epochs
• Rapid interstellar scintillation of PKS B1257-326: two-station pattern time delays and constraints on scattering and microarcsecond source structure

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• The MASIV Survey IV: relationship between intra-day scintillation and intrinsic variability of radio AGNs
• Optical and radio astrometry of the galaxy associated with FRB150418
• The effects of frequency-dependent quasar variability on the celestial reference frame
• Observational tests of the picture of disk accretion
• Microarcsecond structure of an AGN Jet via Interstellar Scintillation