Multi-Wavelength Radiation and Polarization Signatures from Relativistic Magnetic Reconnection in Blazars

Blazars are relativistic plasma jet that point very close to our line of sight. They are launched from supermassive black holes, initially consisting of mostly magnetic energy. They exhibit highly variable multi-wavelength emission from an unresolved region, often referred to as the blazar zone. The recent IceCube detection of a very high energy neutrino event coincident with the blazar TXS 0506+056 flare suggests that blazars can also be the origin of extragalactic cosmic rays and neutrinos. These phenomena imply extreme particle acceleration in very localized region. Relativistic magnetic reconnection is an efficient physical mechanism to accelerate particles in highly magnetized plasma. Here we present combined particle-in-cell and polarized radiation transfer simulations to study multi-wavelength radiation and polarization signatures from reconnection in the blazar zone environment. Our results reveal several very interesting observable trends: 1. both low- and high-energy spectral components show an overall harder-when-brighter trend; 2. gamma-rays show fast flares; 3. higher-energy bands tend to be more variable; 4. optical polarization angle swings are correlated to gamma-ray flares; 5. X-ray polarization angle can swing during flares. In the hadronic scenario, reconnection may lead to considerable enhancement of cosmic ray acceleration and neutrino production in local regions, which may explain the TXS 0506+056 event. These features can be examined by Fermi, optical polarimeters, and future high-energy polarimeters such as IXPE and AMEGO-X.