Low-frequency radio observations of recurrent nova RS Ophiuchi with MeerKAT and LOFAR

We report low-frequency radio observations of the 2021 outburst of the recurrent nova RS Ophiuchi. These observations include the lowest frequency observations of this system to date. Detailed light curves are obtained by MeerKAT at 0.82 and 1.28 GHz and LOFAR at 54 and 154 MHz. These low-frequency detections allow us to put stringent constraints on the brightness temperature that clearly favour a non-thermal emission mechanism. The radio emission is interpreted and modelled as synchrotron emission from the shock interaction between the nova ejecta and the circumbinary medium. The light curve shows a plateauing behaviour after the first peak, which can be explained by either a non-uniform density of the circumbinary medium or a second emission component. Allowing for a second component in the light-curve modelling captures the steep decay at late times. Furthermore, extrapolating this model to 15 yr after the outburst shows that the radio emission might not fully disappear between outbursts. Further modelling of the light curves indicates a red giant mass-loss rate of similar to 5 x 10(-8) M(circle dot)yr(-1). The spectrum cannot be modelled in detail at this stage, as there are likely at least four emission components. Radio emission from stellar wind or synchrotron jets is ruled out as the possible origin of the radio emission. Finally, we suggest a strategy for future observations that would advance our understanding of the physical properties of RS Ophiuchi.

Automated summary

We present low-frequency radio observations of the recurrent nova RS Ophiuchi in 2021, including the lowest frequency observations to date. The radio emission is interpreted as synchrotron emission from the shock interaction between the nova ejecta and the circumbinary medium. The light curve shows plateauing behavior after the initial peak, which can be explained by a non-uniform density of the circumbinary medium or a second emission component. Modeling of the light curves suggests a red giant mass-loss rate of about 5 x 10^(-8) solar masses. Future observations are proposed to further advance our understanding of RS Ophiuchi's physical properties.