Oral Presentation
Constraining AGN Jets with Spectrum and Core Shift: The Case of M87
Presenter: Kouichi Hirotani (ASIAA)
We apply our post-processing radiative-transport code, R-JET, to the M87 jet.
Using very-long-baseline interferometry (VLBI) observations and published
general relativistic magnetohydrodynamic simulations, we constrain the
evolution of the bulk Lorentz factor, the magnetization parameter, and
the magnetic field strength along the jet. We then infer the electron density,
emission coefficient, and absorption coefficient at each point, and compute
the spectral energy distribution (SED) and the coreshift of the synchrotron
emission from the relativistic jet. We find that the jet becomes
limb-brightened by virtue of the angle-dependent energy extraction from
the rotating black hole (BH), and that the jet-forming region exhibits
a ring-like structure if we observe the jet nearly face-on. It is also found
that the jet-launching region is located around seven Schwarzschild radii
from the BH, that the M87 jet is likely composed of a pair plasma, and
that the jet flowline geometry is quasi-parabolic as reported at much
greater distances.
We also discuss that contemporaneous observations of the M87 jet with
ALMA and VLBI could discriminate the jet composition and its collimation
within the central 100 Schwarzschild radii. For example, lower frequency
range (ALMA band 1) is important to find the deviation from a flat-top
spectrum (below 20 GHz) to an inverted spectrum (above 20 GHz).
Middle frequency range (bands 2-8) constrains the curvature of the thermal
component. The higher frequency range (bands 9-10) is important to constrain
the frequency of the inflection point, which is formed between the
thermal-component dominance (in lower frequencies) and
the nonthermal-component dominance (in higher frequencies).
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