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 $\Gamma \gtrsim 10$ within one parsec distance from the central engine. The acceleration slows down but continues at larger distances, with intrinsic acceleration rate $\dot{\Gamma}/\Gamma$ between $0.0005~\rm{yr^{-1}}$ and $0.005~\rm{yr^{-1}}$ 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 $\nu_{\rm peak}$ is anti-proportional to the location of the peak of the dissipation, which is set by the minimal stripe width $l_{\rm min}$. 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.