Radiation and Polarization Signatures from Magnetic Reconnection in Relativistic Jets--II. Connection with $\gamma$-rays

TL;DR

This study uses advanced simulations to connect magnetic reconnection in relativistic jets with observable multi-wavelength and polarization signatures, explaining correlated gamma-ray and optical flares in blazars.

Contribution

It presents the first direct evaluation of gamma-ray signatures from first-principle simulations of magnetic reconnection in blazar jets, linking physical processes to observable emissions.

Findings

Optical and gamma-ray bands show harder-when-brighter trends.

Optical polarization swings are correlated with gamma-ray flares.

Inhomogeneous particle distributions cause variable synchrotron self-Compton signatures.

Abstract

It is commonly believed that blazar jets are relativistic magnetized plasma outflows from supermassive black holes. One key question is how the jets dissipate magnetic energy to accelerate particles and drive powerful multi-wavelength flares. Relativistic magnetic reconnection has been proposed as the primary plasma physical process in the blazar emission region. Recent numerical simulations have shown strong acceleration of nonthermal particles that may lead to multi-wavelength flares. Nevertheless, previous works have not directly evaluated $\gamma$-ray signatures from first-principle simulations. In this paper, we employ combined particle-in-cell and polarized radiation transfer simulations to study multi-wavelength radiation and optical polarization signatures under the leptonic scenario from relativistic magnetic reconnection. We find harder-when-brighter trends in optical and {\it Fermi-LAT} $\gamma$-ray bands as well as closely correlated optical and $\gamma$-ray flares. The optical polarization angle swings are also accompanied by $\gamma$-ray flares with trivial time delays. Intriguingly, we find highly variable synchrotron self Compton signatures due to inhomogeneous particle distributions during plasmoid mergers. This feature may result in fast $\gamma$-ray flares or orphan $\gamma$-ray flares under the leptonic scenario, complementary to the frequently considered mini-jet scenario. It may also infer neutrino emission with low secondary synchrotron flux under the hadronic scenario, if plasmoid mergers can accelerate protons to very high energy.