Propagation of cosmic rays in plasmoids of AGN jets -- implications for multimessenger predictions

TL;DR

This paper analyzes how cosmic rays propagate in AGN jet plasmoids, revealing a transition between diffusive and ballistic regimes that impacts multiwavelength and neutrino emission predictions.

Contribution

It provides a quantitative analysis of cosmic ray transport regimes in relativistic plasmoids, enhancing understanding of multi-messenger signals from AGN jets.

Findings

Transition between diffusive and ballistic propagation affects emission spectra.

Propagation regimes significantly influence blazar flare lightcurves.

Modeling cosmic ray transport is crucial for interpreting multi-messenger observations.

Abstract

After the successful detection of cosmic high-energy neutrinos, the field of multiwavelength photon studies of active galactic nuclei (AGN) is entering an exciting new phase. The first hint of a possible neutrino signal from the blazar TXS 0506+056 leads to the anticipation that AGN could soon be identified as point sources of high-energy neutrino radiation, representing another messenger signature besides the well-established photon signature. To understand the complex flaring behavior at multiwavelengths, a genuine theoretical understanding needs to be developed. These observations of the electromagnetic spectrum and neutrinos can only be interpreted fully when the charged, relativistic particles responsible for the different emissions are modeled properly. The description of the propagation of cosmic rays in a magnetized plasma is a complex question that can only be answered when analysing the transport regimes of cosmic rays in a quantitative way. In this paper, we therefore present a quantitative analysis of the propagation regimes of cosmic rays in the approach that is most commonly used to model non-thermal emission signatures from blazars, i.e. the existence of a high-energy cosmic-ray population in a relativistic plasmoid traveling along the jet axis. In this paper, we show that in the considered energy range of high-energy photon and neutrino emission, the transition between diffusive and ballistic propagation takes place, significantly influencing not only the spectral energy distribution but also the lightcurve of blazar flares.