Magnetization degree at the jet base of M87 derived from the event horizon telescope data: Testing magnetically driven jet paradigm

M. Kino; F. Takahara; K. Hada; K. Akiyama; H. Nagai; B. W. Sohn

doi:10.1088/0004-637X/803/1/30

paper

Magnetization degree at the jet base of M87 derived from the event horizon telescope data: Testing magnetically driven jet paradigm

arXiv:1502.03900 · doi:10.1088/0004-637X/803/1/30

Abstract

We explore the degree of magnetization at the jet base of M87 by using the observational data of the event horizon telescope (EHT) at 230~GHz obtained by Doeleman et al. By utilizing the method in Kino et al., we derive the energy densities of magnetic fields ( $U_{B}$ ) and electrons and positrons ( $U_{\pm}$ ) in the compact region detected by EHT (EHT-region) with its full-width-half-maximum size $40 μ as$ . First, we assume that an optically-thick region for synchrotron self absorption (SSA) exists in the EHT-region. Then, we find that the SSA-thick region should not be too large not to overproduce the Poynting power at the EHT-region. The allowed ranges of the angular size and the magnetic field strength of the SSA-thick region are $21 μ as \leq θ_{thick} \leq 26.3 μ as$ and $50 G \leq B_{tot} \leq 124 G$ , respectively. Correspondingly $U_{B} ≫ U_{\pm}$ is realized in this case. We further examine the composition of plasma and energy density of protons by utilizing the Faraday rotation measurement ( $R M$ ) at 230~GHz obtained by Kuo et al. Then, we find that $U_{B} ≫ U_{\pm} + U_{p}$ still holds in the SSA-thick region. Second, we examine the case when EHT-region is fully SSA-thin. Then we find that $U_{B} ≫ U_{\pm}$ still holds unless protons are relativistic. Thus, we conclude that magnetically driven jet scenario in M87 is viable in terms of energetics close to ISCO scale unless the EHT-region is fully SSA-thin and relativistic protons dominated.

14 pages, 5 figures, 3 tables, accepted for publication in ApJ

Magnetization degree at the jet base of M87 derived from the event horizon telescope data: Testing magnetically driven jet paradigm

Abstract

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