The Symbiotic Recurrent Nova V745 Sco at Radio Wavelengths

V745 Sco is a Galactic symbiotic recurrent nova with nova eruptions in 1937, 1989, and 2014. We study the behaviour of V745 Sco at radio wavelengths (0.6-37 GHz), covering both its 1989 and 2014 eruptions and informed by optical, X-ray, and gamma-ray data. The radio light curves are synchrotron-dominated. Surprisingly, compared to expectations for synchrotron emission from explosive transients such as radio supernovae, the light curves spanning 0.6-37 GHz all peak around the same time (similar to 18-26 d after eruption) and with similar flux densities (5-9 mJy). We model the synchrotron light curves as interaction of the nova ejecta with the red giant wind, but find that simple spherically symmetric models with wind-like circumstellar material (CSM) cannot explain the radio light curve. Instead, we conclude that the shock suddenly breaks out of a dense CSM absorbing screen around 20 d after eruption, and then expands into a relatively low-density wind (M-out(center dot)approximate to 10(-9)-10(-8) M-circle dot yr(-1) for v(w)=10 km s(-1)) out to similar to 1 yr post-eruption. The dense, close-in CSM may be an equatorial density enhancement or a more spherical red giant wind with M-in(center dot)approximate to[5-10]x10(-7) M-circle dot yr(-1), truncated beyond several x10(14) cm. The outer lower-density CSM would not be visible in typical radio observations of Type Ia supernovae: V745 Sco cannot be ruled out as a Type Ia progenitor based on CSM constraints alone. Complementary constraints from the free-free radio optical depth and the synchrotron luminosity imply the shock is efficient at accelerating relativistic electrons and amplifying magnetic fields, with & varepsilon;(e) and & varepsilon;(B )approximate to 0.01-0.1.