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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 (⁠|$\sim$| 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 (⁠|$\dot{M}_{out} \approx 10^{-9}\!-\!10^{-8}$|  M |$_{\odot }$|  yr |$^{-1}$| for |$v_w = 10$|  km s |$^{-1}$|⁠) out to |$\sim$| 1 yr post-eruption. The dense, close-in CSM may be an equatorial density enhancement or a more spherical red giant wind with |$\dot{M}_{in} \approx [5\!-\!10] \times 10^{-7}$| M |$_{\odot }$| yr |$^{-1}$|⁠ , truncated beyond several |$\times 10^{14}$|  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 |$\epsilon _e$| and |$\epsilon _B \approx 0.01\!-\!0.1$|⁠. [ABSTRACT FROM AUTHOR]

Superbubbles are crucial for stellar feedback, with supposedly high (of the order of 10 per cent) thermalization rates. We combined multiband radio continuum observations from the Very Large Array (VLA) with Effelsberg data to study the non-thermal superbubble (NSB) in IC 10, a starburst dwarf irregular galaxy in the Local Group. Thermal emission was subtracted using a combination of Balmer Hα and VLA 32 GHz continuum maps. The bubble's non-thermal spectrum between 1.5 and 8.8 GHz displays curvature and can be well fitted with a standard model of an ageing cosmic ray electron population. With a derived equipartition magnetic field strength of 44 ± 8 μG, and measuring the radiation energy density from Spitzer MIPS maps as 5 ± 1 × 10−11 erg cm−3, we determine, based on the spectral curvature, a spectral age of the bubble of 1.0 ± 0.3 Myr. Analysis of the LITTLE THINGS H i data cube shows an expanding H i hole with 100 pc diameter and a dynamical age 3.8 ± 0.3 Myr, centred to within 16 pc on IC 10 X-1, a massive stellar mass black hole (M > 23 M⊙). The results are consistent with the expected evolution for a superbubble with a few massive stars, where a very energetic event like a Type Ic supernova/hypernova has taken place about 1 Myr ago. We discuss alternatives to this interpretation. [ABSTRACT FROM PUBLISHER]

Very-long-baseline interferometry observations have revealed a bright, compact radio component near the center of the expanding shell of supernova 1986J. The component, not present in earlier images, has an inverted radio spectrum different from that of the shell. Such an inversion has not been seen in the spectrum of any other supernova. The new component is likely radio emission associated either with accretion onto a black hole or with the nebula formed around an energetic young neutron star in the center of SN 1986J, which would directly link either a black hole or a neutron star to a modern supernova. [ABSTRACT FROM AUTHOR]

Novae, which are the sudden visual brightening triggered by runaway thermonuclear burning on the surface of an accreting white dwarf, are fairly common and bright events. Despite their astronomical significance as nearby laboratories for the study of nuclear burning and accretion phenomena, many aspects of these common stellar explosions are observationally not well-constrained and remain poorly understood. Radio observations, modeling and interpretation can potentially play a crucial role in addressing some of these puzzling issues. In this review on radio studies of novae, we focus on the possibility of testing and improving the nova models with radio observations, and present a current status report on the progress in both the observational front and theoretical developments. We specifically address the issues of accurate estimation of ejecta mass, multi-phase and complex ejection phenomena, and the effect of a dense environment around novae. With highlights of new observational results, we illustrate how radio observations can shed light on some of these long-standing puzzles. [ABSTRACT FROM AUTHOR]