Shock-driven synchrotron radio emission from the 2021 outburst of RS Ophiuchi

Abstract

We present low-frequency radio observations of the Galactic symbiotic recurrent nova RS Ophiuchi during its 2021 outburst. The observations were carried out with the upgraded Giant Metrewave Radio Telescope spanning a frequency range of 0.15-1.4 GHz during 23-287 d post the outburst. The average value of the optically thin spectral index is α ~ -0.4 (F_ν ∝ ν^α), indicating a non-thermal origin of the radio emission at the observed frequencies. The radio light curves are best represented by shock-driven synchrotron emission, initially absorbed by a clumpy ionized circumbinary medium. We estimate the mass-loss rate of the red giant companion star to be $\dot{M} \sim$ 7.5 × 10^-8 M_⊙ yr^-1 for an assumed stellar wind velocity of 20 km s^-1. The 0.15-1.4 GHz radio light curves of the 2021 outburst are systematically brighter than those of the 2006 outburst. Considering similar shock properties between the two outbursts, this is indicative of a relatively higher particle number density in the synchrotron emitting plasma in the current outburst.