Radiation Signatures From Striped Blazar Jet

Abstract

Relativistic jets from supermassive black holes are among the most powerful and luminous astrophysical systems in Universe. We propose that the open magnetic field lines through the black hole, which drive a strongly magnetized jet, may have their polarity reversing over time scales related to the growth of the magneto-rotational dynamo in the disc, resulting in dissipative structures in the jet characterized by reversing toroidal field polarities, referred to as "stripes". Magnetic reconnection between the stripes dissipates the magnetic energy and powers jet acceleration. The striped jet model can explain the jet acceleration, large-scale jet emission, and blazar emission signatures consistently in a unified physical picture. Specifically, we find that the jet accelerates to the bulk Lorentz factor Γ 10 within one parsec distance from the central engine. The acceleration slows down but continues at larger distances, with intrinsic acceleration rate Γ/Γ between 0.0005 yr −1 and 0.005 yr −1 at tens of parsecs, which is in very good agreement with recent radio observations. Magnetic reconnection continuously accelerates nonthermal particles over large distances from the central engine, resulting in the core-shift effect and overall flat-to-inverted synchrotron spectrum. The large-scale spectral luminosity peak 𝜈 peak is anti-proportional to the location of the peak of the dissipation, which is set by the minimal stripe width 𝑙 min . The blazar zone is approximately at the same location. At this distance, the jet is moderately magnetized, with the comoving magnetic field strength and dissipation power consistent with typical leptonic blazar model parameters.

Identifying changing jets through their radio variability

“…Alternatively, acceleration at parsecs scales in a conical geometry can occur in a striped jet model with reversing toroidal magnetic field polarities (Zhang & Giannios 2021). In this case, jet acceleration is powered by magnetic energy dissipation via magnetic reconnection between stripes and can continue even after tens of parsecs from the black hole.…”

“…Whether the jets are launched with such high Γ or are accelerated to the velocities measured at parsec scales is still an open quesyannis.liodakis@utu.fi tion. Most likely the jets are highly magnetized when launched and are accelerated through the conversion of magnetic to kinetic energy (Vlahakis & Königl 2004;Vlahakis 2004;Komissarov et al 2007;Zhang & Giannios 2021). The jet is confined by either magnetic hoop stress (e.g., Spruit et al 1997) or the pressure of the external medium (Lyubarsky 2009(Lyubarsky , 2010Liodakis 2018) into a parabolic shape which favors acceleration.…”