Radiation and Polarization Signatures from Magnetic Reconnection in Relativistic Jets. I. A Systematic Study

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 γ-ray signatures from first-principle simulations. In this paper, we employ combined particle-in-cell and polarized radiation transfer simulations to study multiwavelength radiation and optical polarization signatures under the leptonic scenario from relativistic magnetic reconnection. We find harder-when-brighter trends in optical and Fermi-LAT γ-ray bands as well as closely correlated optical and γ-ray flares. The optical polarization angle swings are also accompanied by γ-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 γ-ray flares or orphan γ-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.

The complex variability of blazars: time-scales and periodicity analysis in S4 0954+65

“…In particular, wide rotations of the EVPA are often observed (e.g. Marscher et al 2008;Blinov et al 2015Blinov et al , 2016Blinov et al , 2018Hagen-Thorn et al 2015;Gupta et al 2017;Lyutikov & Kravchenko 2017;Raiteri et al 2017a;Zhang et al 2020).…”

Probing Magnetic Fields and Acceleration Mechanisms in Blazar Jets with X-ray Polarimetry

“…From the point of view of polarimetric measurements, it is conceptually important to distinguish between the effects that are related to the small-scale structure of the magnetic field associated with a single current sheet from the imprints of large-scale fields shaped by the macroscopic dynamics of the system. For instance, recent specific PIC studies [72][73][74] focus on the polarimetric properties of the synchrotron radiation produced by particles diffusing in the complex field that is associated with a single current sheet. The derived synthetic lightcurves reveal large (exceeding 50%) and variable polarization fractions and ample variations of the angle of polarization (up to ∆χ = 180 • ).…”

PIC methods in astrophysics: simulations of relativistic jets and kinetic physics in astrophysical systems

“…While the common use cases for VPIC employ low-order particles on rectilinear meshes, a framework exists to treat higher-order particles and curvilinear meshes, as well as more advanced field solvers. VPIC has been used for simulations of reconnections (Guo et al 2020;Zhang et al 2020).…”