Rapid Radio Flaring during an Anomalous Outburst of SS Cyg

TL;DR

This study reports the first observation of a giant radio flare in SS Cyg during an anomalous outburst, revealing rapid plasma ejections and challenging existing accretion-jet models for white dwarf binaries.

Contribution

It provides the first detection of a giant radio flare in SS Cyg, offering new insights into jet activity during dwarf nova outbursts and highlighting differences from X-ray binary behaviors.

Findings

Rapid radio flaring observed throughout the outburst

First detection of a giant radio flare (~20 mJy, 15 min) in SS Cyg

Giant flare occurred during declining accretion rate phase

Abstract

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 we present densely-sampled radio coverage, obtained with the Arcminute MicroKelvin Imager Large Array, of the dwarf nova SS Cyg during its February 2016 anomalous outburst. The outburst displayed a slower rise (3 days per mag) in the optical than typical ones, and lasted for more than 3 weeks. Rapid radio flaring on timescales <1 hour was seen throughout the outburst. The most intriguing behavior in the radio was towards the end of the outburst where a 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 coverage could explain its non-detection in previous outbursts. These data, together with past radio observations, are consistent with synchrotron emission from plasma ejection events as being the origin of the radio flares. However, the production of the giant flare during the declining accretion rate phase remains unexplained within the standard accretion-jet framework and appears to be markedly different to similar patterns of behavior in X-ray binaries.