Probing the Emission Mechanism and Magnetic Field of Neutrino Blazars with Multiwavelength Polarization Signatures

Abstract

The characteristic two-component blazar spectral energy distribution (SED) can be of either leptonic and/or hadronic origins. The potential association of the high-energy neutrino event IceCube-170922A with the flaring blazar TXS 0506+056 indicates that hadronic processes may operate in a blazar jet. Despite multi-wavelength follow-ups of the event and extensive theoretical modelings, the radiation mechanisms and the underlying magnetic field strength and configuration remain poorly understood. In this paper, we consider generic leptonic and hadronic blazar spectral models with distinct magnetic field strengths and radiation mechanisms. We analytically reproduce the SEDs and the neutrino flux of hadronic models, and predict their X-ray to γ-ray polarization degrees. Furthermore, by performing relativistic magnetohydrodynamic (RMHD) simulations taking into account the polarizationdependent radiation transfer, we study the time-dependent multi-wavelength polarization variability of the proton synchrotron model under a shock scenario. Our results suggest that the high-energy polarization degree and the neutrino flux can be jointly used to pinpoint the leptonic and/or hadronic blazar radiation mechanisms in the X-ray and γ-ray bands, and to infer the magnetic field strength in the emission region. Additionally, the temporal multi-wavelength polarization signatures in the proton synchrotron model shed light on the jet energy composition and the dynamical importance of magnetic fields in the blazar emission region. Future multi-wavelength polarimetry facilities such as IXPE and AMEGO together with neutrino telescopes such as IceCube can provide unprecedented observational constraints to probe the blazar radiation mechanisms and jet dynamics.

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

“…This is done through a Compton scattering module that works similarly as the 3DPol code, but without the polarization dependence. This is because the PD due to SSC and EC is generally very low in the blazar emission region, which is unlikely to be observed (Bonometto et al 1970;Paliya et al 2018;Zhang et al 2019;Dreyer & Böttcher 2021). To summarize, we consider two seed photon fields for the Compton scattering in the radiation transfer simulation: an inhomogeneous and fast-evolving synchrotron photon field for the SSC, and a uniform and stationary black body photon field for the EC.…”

“…As a result, in the high state the 0.1 GeV γ-ray band shows a rather flat spectrum dominated by the SSC contribution, but in the low state it exhibits a rising spectrum dominated by the EC contribution (see Figure 2). This issue generally applies to any blazar spectral modeling with multiple radiation processes in the highenergy spectral component, including the lepto-hadronic models (Böttcher et al 2013;Cerruti et al 2019;Zhang et al 2019;Keivani et al 2018), which can be tested with future MeV γ-ray telescopes such as AMEGO (McEnery et al 2019;Rani et al 2019b). We note that our setup targets at a flat-spectrum radio quasar that peaks in the GeV band, and the harder-when-brighter trend is clear around or beyond the peak.…”

“…Alternatively, hadronic emission processes, including proton synchrotron, photomeson, and subsequent cascades, can contribute to the high-energy component (referred to as the hadronic model, see Mannheim 1993;Mücke et al 2003;Böttcher et al 2013). In particular, the recent detection of a very high energy neutrino is potentially correlated with a blazar flare, strongly suggesting the presence of hadronic processes in blazars (IceCube Collaboration et al 2018;Keivani et al 2018;Gao et al 2019;Cerruti et al 2019;Reimer et al 2019;Zhang et al 2019). It has been suggested that X-ray to MeV γ-ray polarimetry can independently diagnose the contribution of hadronic processes in the high-energy spectral component (Zhang & Böttcher 2013;Zhang et al 2016;Zhang 2017;Paliya et al 2018), which may be detected by the upcoming IXPE 1 as well as future MeV γ-ray telescopes such as AMEGO (McEnery et al 2019;Rani et al 2019a).…”

Blazar Optical Polarimetry: Current Progress in Observations and Theories

“…Since the optical and high-energy emissions are likely from the same emission region, they should share the same magnetic field morphology. In this situation, [52,107] have shown that the high-energy polarization degree may be detectable with high-energy polarimeters, which can distinguish the leptonic and hadronic models (see Figure 9 left). [109] has studied the temporal behavior of multi-wavelength polarization signatures.…”

“…However, the very dynamical and complex nature of AGN jets prevents the use of simple analytical models. Recent first-principle numerical simulations have attempted to consistently combine plasma dynamics and radiation processes to directly compare with observations [88,98,104,105,107], which have shown interesting predictions in polarization variability. With the development of CPU and GPU computing in the next decade, this multi-physics approach will revolutionize our understanding of jet dynamics.…”