| Résumé | Radio emission from non-magnetic cataclysmic variables (CVs, accreting white dwarfs) could allow detailed studies of outflows and possibly accretion flows in these nearby, numerous and non-relativistic compact accretors. Up to now, however, very few CVs have been detected in the radio. We have conducted a Very Large Array pilot survey of four close and optically bright novalike CVs at 6 GHz, detecting three, and thereby doubling the number of radio detections of these systems. TT Ari, RW Sex and the old nova V603 Aql were detected in both of the epochs, while V1084 Her was not detected (to a 3σ upper limit of 7.8 μJy beam-1). These observations clearly show that the sensitivity of previous surveys was typically too low to detect these objects and that non-magnetic CVs can indeed be significant radio emitters. The three detected sources show a range of properties, including flaring and variability on both short (~200 s) and longer term (days) time-scales, as well as circular polarization levels of up to 100 per cent. The spectral indices range from steep to inverted; TT Ari shows a spectral turnover at ~6.5 GHz, while the spectral index of V603 Aql flattened from α = 0.54 ± 0.05 to 0.16±0.08 (F<inf>ν</inf> ∞ να) in the week between observations. This range of properties suggests that more than one emission process can be responsible for the radio emission in non-magnetic CVs. In this sample we find that individual systems are consistent with optically thick synchrotron emission, gyrosynchrotron emission or cyclotron maser emission. |
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