Rapid Radio Flaring during an Anomalous Outburst of SS Cyg

The connection between accretion and jet production in accreting white dwarf binary systems, especially dwarf novae, is not well understood. Radio wavelengths provide key insights into the mechanisms responsible for accelerating electrons, including jets and outflows. Here wepresent densely sampled radio coverage, obtained with the Arcminute MicroKelvin ImagerLarge Array, of the dwarf nova SS Cyg during its February 2016 anomalous outburst. Theoutburst displayed a slower rise (3 days mag&#x100000;1) in the optical than typical ones, and lastedfor more than 3 weeks. Rapid radio flaring on timescales <1 hour was seen throughout theoutburst. The most intriguing behavior in the radio was towards the end of the outburst wherea fast, luminous (“giant”), flare peaking at 20 mJy and lasting for 15 minutes was observed.This is the first time that such a flare has been observed in SS Cyg, and insufficient coveragecould explain its non-detection in previous outbursts. These data, together with past radioobservations, are consistent with synchrotron emission from plasma ejection events as beingthe origin of the radio flares. However, the production of the giant flare during the decliningaccretion rate phase remains unexplained within the standard accretion-jet framework andappears to be markedly different to similar patterns of behavior in X-ray binaries.