Late-outburst radio flaring in SS Cyg and evidence for a powerful kinetic output channel in cataclysmic variables

TL;DR

This study reports late-outburst radio flaring in the dwarf nova SS Cyg, revealing that such flares are common and likely originate from jets, indicating a significant kinetic energy output in cataclysmic variables.

Contribution

The paper provides new radio observations of SS Cyg showing late-outburst flaring and analyzes the physical conditions, suggesting jet formation as a key energy channel in cataclysmic variables.

Findings

Late-outburst radio flaring occurs during optical flux decay.

Synchrotron-emitting plasma expands at about 1% of light speed.

Jet activity likely carries away significant accretion energy.

Abstract

Accreting white dwarfs in binary systems known as cataclysmic variables (CVs) have in recent years been shown to produce radio flares during outbursts, qualitatively similar to those observed from neutron star and black hole X-ray binaries, but their ubiquity and energetic significance for the accretion flow has remained uncertain. We present new radio observations of the CV SS Cyg with Arcminute Microkelvin Imager Large Array, which show for the second time late-ouburst radio flaring, in April 2016. This flaring occurs during the optical flux decay phase, about ten days after the well-established early-time radio flaring. We infer that both the early- and late-outburst flares are a common feature of the radio outbursts of SS Cyg, albeit of variable amplitudes, and probably of all dwarf novae. We furthermore present new analysis of the physical conditions in the best-sampled late-outburst flare, from Feb 2016, which showed clear optical depth evolution. From this we can infer that the synchrotron-emitting plasma was expanding at about 1% of the speed of light, and at peak had a magnetic field of order 1 Gauss and total energy content > 10^{33} erg. While this result is independent of the geometry of the synchrotron-emitting region, the most likely origin is in a jet carrying away a significant amount of the available accretion power.