Radio component of the multi-messenger emission from the anticipated T Coronae Borealis outburst

Abstract

T Coronae Borealis is the nearest symbiotic recurrent nova and is expected to undergo a new eruption soon, offering a rare opportunity to study shock evolution and particle acceleration. We predict radio emission from the outburst and assess how radio observations can constrain the circumbinary medium (CBM) and cosmic-ray acceleration. We post-process three-dimensional (3D) hydrodynamic nova simulations with a multi-zone model for particle acceleration and radio emission, computing thermal free-free and non-thermal synchrotron radiation, including the Razin effect and free-free and synchrotron self-absorption for different CBM configurations. Early radio morphology should not be interpreted directly as the intrinsic shock geometry, because free-free absorption selectively obscures regions of the 3D emitting volume. The intrinsic radio emission is dominated by synchrotron radiation from electrons accelerated at the forward shock, with unabsorbed fluxes reaching 100-1000 Jy at GHz frequencies during the first day. Dense ejecta and shocked CBM material strongly absorb the emission, reducing the observable flux by several orders of magnitude. The source becomes largely transparent at GHz frequencies within about one month. Radio emission remains predominantly non-thermal during the first year, while thermal emission becomes important only for dense equatorial enhancements. The radio spectral index evolves from positive values caused by absorption to the optically thin synchrotron value of about 0.5 after several weeks. A short-lived polarized signal may arise during the first few days if the red giant's magnetic field contributes to the cosmic-ray-generated field. Early multi-frequency radio monitoring and polarimetry of the forthcoming T CrB eruption will probe density structure and magnetic field, testing particle acceleration in symbiotic recurrent novae.