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2020-10-11 Abstract

Title: Collimation and Acceleration of the M87 jet (and more)
 
Speaker:  Dr. Jongho Park (ASIAA)
 
Date: December 11 at 14:30
 
Location: R521, General Building II
 
Abstract: 

It is widely accepted that relativistic jets in AGNs are accelerated by strong magnetic fields. The magnetohydrodynamic (MHD) models of jet acceleration predict that (i) jet is gradually collimated by the pressure of an external medium confining the jet and (ii) jet collimation and acceleration occur simultaneously. Indeed, systematic collimation has been revealed in the jet of M87 inside the Bondi radius by many recent very long baseline interferometry observations. However, both the nature of the external confining medium and the presence of gradual jet acceleration in the jet collimation zone have not been well constrained by observations. In the first part of my talk, I briefly introduce our recent study of Faraday rotation in the M87 jet, where information on the external medium is imprinted. We found that the magnitude of the Faraday rotation measure systematically decreases with increasing distance from the black hole in the jet collimation zone. Our data is consistent with a picture that substantial winds, non-relativistic un-collimated gas outflows launched from hot accretion flows, confine the jet, resulting in the observed jet collimation. In the second part, I present the results of our recent kinematic analysis of the high-cadence monitoring data observed with the East Asian VLBI Network (EAVN) and of the Very Long Baseline Array (VLBA) archival data. We found that the jet is gradually accelerated from non-relativistic to relativistic speeds over a broad distance range that coincides with the jet collimation zone, which is in good agreement with the prediction of the MHD models. I also present the results of my recent work on another nearby radio galaxy NGC 315, which shows a very similar trend of jet collimation and acceleration to M87.

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