Abstract
We investigate the structure and dynamics of the M87 jet based on multi-frequency VLBI observations and MHD jet theories. Millimeter VLBI cores are considered as innermost jet emissions. The jet structure up to ~ 105 r s is described as a parabolic streamline, indicating the lateral expansion under a confinement by the stratified ISM. Thus, the jet collimation maintains in five orders of magnitude in the distance starting from the vicinity of the supermassive black hole (SMBH), less than 10 r s . We here examine the jet parabolic structure in order to identify the property of a bulk acceleration; observed sub-to-superluminal motions indicate an MHD acceleration from non-relativistic to relativistic regimes. We propose that the M87 jet consists of Poynting-flux dominated flows, powered by nonlinear torsional Alfven waves. Future sub-mm VLBI observations play an important role in resolving the origin of the M87 jets.
Highlights
How do the acceleration and collimation, as well as the formation process, take place in astrophysical jets? electromagnetic and/or magnetohydrodynamic (MHD) mechanisms are frequently invoked to extract energy and momentum from the compact object and/or the accretion disk [e.g., 1–5], none of the real astrophysical jet systems have yet been examined to confirm these theoretical properties in a quantitative manner.M 87 is one of the nearest active galaxies [16.7 Mpc; 6] that exhibit relativistic outflows
We remark that the size of the very long baseline interferometry (VLBI) core at 230 GHz is derived by the EHT observation as 5.5 ± 0.4 rs in the correlated flux density analysis by circular Gaussian models [30]
Current innermost emissions of the M87 jet lie at ∼ few ×102 rs from the central supermassive black hole (SMBH), which have been observed by 43 GHz VLBA observations
Summary
How do the acceleration and collimation, as well as the formation process, take place in astrophysical jets? electromagnetic and/or magnetohydrodynamic (MHD) mechanisms are frequently invoked to extract energy and momentum from the compact object and/or the accretion disk [e.g., 1–5], none of the real astrophysical jet systems have yet been examined to confirm these theoretical properties in a quantitative manner. There have been several attempts to examine the inner jet structures on M87: i) Hada et al (2011) [27] performed the core shift measurement by using multifrequency, phase-referencing Very Long Baseline Array (VLBA) observations, indicating that the 43 GHz VLBI core is located at ∼ 20 rs from the central engine (presumably, the SMBH and/or accretion disk). They conclude that the measured frequency dependence of the core shift ∝ ν−0.94±0.09 is in good agreement with a synchrotron selfabsorbed jet [23, 28]. Note that 1 mas corresponds to 517 rs in de-projection
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