Modeling radio circular polarization in the Crab nebula

Abstract

In this paper we present, for the first time, simulated maps of the circularly polarized synchrotron emission from the Crab nebula, using multidimensional state of the art models for the magnetic field geometry. Synchrotron emission is the signature of non-thermal emitting particles, typical of many high-energy astrophysical sources, both Galactic and extra-galactic ones. Its spectral and polarization properties allow us to infer key informations on the particles distribution function and magnetic field geometry. In recent years our understanding of pulsar wind nebulae has improved substantially thanks to a combination of observations and numerical models. A robust detection or non-detection of circular polarization will enable us to discriminate between an electron-proton plasma and a pair plasma, clarifying once for all the origin of the radio emitting particles, setting strong constraints on the pair production in pulsar magnetosphere, and the role of turbulence in the nebula. Previous attempts at measuring the circular polarization have only provided upper limits, but the lack of accurate estimates, based on reliable models, makes their interpretation ambiguous. We show here that those results are above the expected values, and that current polarimetric tecniques are not robust enough for conclusive result, suggesting that improvements in construction and calibration of next generation radio facilities are necessary to achieve the desired sensitivity.

A laminar model for the magnetic field structure in bow-shock pulsar wind nebulae

“…8), with a polarized fraction of 40-50%, and extending for several parsecs. Using the subgrid model by Bandiera & Petruk (2016) recently applied to PWNe (Bucciantini et al 2017;Bucciantini & Olmi 2018), we can estimate a typical turbulence with δB/B ∼ 0.3. On the other hand low polarization systems like the Mouse G359.23-0.82 (Yusef-Zadeh & Gaensler 2005), with polarized fraction below 10% are likely characterized by strong turbulence, in part already evident in the rapid change of polarization pattern.…”

Induced circular polarization on photons due to interaction with axion-like particles in rotating magnetic field of neutron stars

“…(3.9) and numerically solve it. The obtained value of V (t)/I(t) at t = τ /2 is then compared to the minimum detectable circular polarization (V /I) min = 0.01 [48,49]. If the value is discernible, the corresponding m and g aγγ are exported to construct the excluded JCAP04(2024)069 The plot illustrates the parameter space that can be excluded based on the observed circular polarization effect.…”

Synchrotron Polarization Radiative Transfer: Relativistic Thermal Electron Contribution

“…We note that the hybrid thermal/nonthermal electron energy distribution and the strong absorption of polarized photons in our model should be important when we suggest to perform Event Horizon Telescope (EHT) polarization observations. The circular polarization of pulsar wind nebula (PWN) can also be further checked if we consider the thermal electron contribution (Bucciantini & Olmi 2018). We may even consider performing our model for the diffuse synchrotron emission if the electrons in the interstellar medium also have a thermal component (Herron et al 2018).…”