A classical nova is a thermonuclear transient in a compact, accreting binary system known as a cataclysmic variable. In a binary system of a white dwarf and a companion star, outflowing gas from the companion star can transfer to the white dwarf.  These materials accumulate on the surface of the white dwarf, and as the temperature and density increase, an unstable thermonuclear runaway can be the triggered causing the system to suddenly become much brighter at optical wavelengths. Majumder et al. present a search for radio emission from classical novae at 887.5 MHz using data from the ASKAP Variable And Slow Transient (VAST) survey. The team cross-matched 43 optically discovered classical novae that erupted between 2021 September and 2025 November and found three which show significant radio emission: V6598 Sgr, V1716 Sco, and V1723 Sco. All three novae show evidence of non-thermal synchrotron emission as the dominant emission mechanism at this frequency.  Strong early-time synchrotron emission is firm evidence of shock-driven particle acceleration, which may be related to detections of gamma-rays from all three novae as well.

The plots above show optical (top) and radio (bottom) light curves for V6598 Sgr, and V1716 Sco. (The numerically smaller an optical magnitude, the brighter the object is.) Optical data are from AAVSO; radio data at 887.5 MHz are from ASKAP VAST. Triangles indicate 5σ upper limits. V6598 Sgr was reported in the visible band on 2023 July 15, following a rapid rise of > 3 mag within < 24 hours.  The initial brightness was already near the maximum of 10 mag and dropped to 12.5 mag in ~2 days. V1716 Sco was discovered on 2023 April 18 with a rapid rise from 12.5 to 7.3 mag within two days. It then decreased by 2 to 3 mag in the next 15 to 20 days, making it comparatively a very fast nova. The radio flux density rose rapidly, reaching a peak of just over 9 mJy on day 107, before declining. The optical peak precedes the radio rise by ~65 days.