Radio emission from dwarf novae outbursts

Elmar Koerding, Michael Rupen, Christian Knigge, Rob Fender, Vivek Dhawan



Scientific background:

oon of a CVMost accreting sources show transient jets (collimated outflows of gas) during some phases of their life: black hole X-ray binaries (XRBs), neutron star XRBs, Active Galactic Nuclei (AGN: the central black holes of galaxies) but also young stellar objects (proto-stars that are still accreting some of its gas). The only major exception was thought to be cataclysmic variables (CVs of dwarf-novae type, see picture). Usually, it is possible to find these jets with radio observations. However, in the 1980s a large sample of dwarf novae had been observed and only a few radio detection have been reported. Most of the detection could not be reproduced, so people more or less stopped looking.

XRBs and CVs share many properties of their accretion flow. Based on the analogy between these two classes of accreting sources, we have suggested that CVs should show transient radio emission, especially during the rise of the outburst. This has been confirmed by several radio detections of SS Cyg during our recent campaign to observe CVs in outburst (AAVSO Alert Notice 345). The results have been published in the Science magazine (320, 2008 see also the preprint on arxiv). In the following campaign we were able to reproduce the results showing that SS Cyg usually shows radio emission during its outburst.

We would like to thank all observers who helped with observations and alerts! Without your observations this work would not be possible.

While we have now established that SS Cyg shows radio emission we would like to explore whether this is also seen in other CVs. No other CV has a detailed radio-lightcurve, in some cases only a few detections are known.


New radio observations:

We have obtained observation time at the Very Large Array (VLA) to study 4 CV outbursts in detail: Initial detection + subsequent radio monitoring.

As already mentioned, the brightest radio emission is expected to be seen during the beginning of the outburst (rise + beginning of the plateau phase). Thus, it is crucial that we obtain a trigger from the amateur community as fast as possible. It would be ideal if we could get a trigger within 6 hours of the onset of the outburst. Even if the outburst is slightly older than than, we would still like to know about them and will decide on an individual basis if we can observe them or not. 
Once we trigger the radio observations it will be checked if the VLA can observe within a reasonable amount of time. The problem is, that the majority of radio observations are scheduled long before the actual observation is done. Thus, there may not be a long enough 'gap' in the existing schedule to allow for our observation.

Request for observations:

We request observations of our target sources (currently Z Cam, YZ Cnc and EM Cyg) to find the onset of the optical outburst. We therefore request that all detections are submitted to the AAVSO as fast as possible, if any source seems to go into outburst. To avoid false triggers, we will only trigger if two independent observers confirm that the source reached its threshold. If you notice that there is a single observation claiming the onset of an outburst, we would be grateful if you could observe the source to confirm.

We will follow the AAVSO news-flash and should receive any observation you submit to the AAVSO. In case that you are the second observer confirming an outburst, you can directly alert us (in addition to submitting your observation to the AAVSO) by sending an email to CVs (at) (alerts only!)
If you have any questions or comments please email me at elmar (at)  I will update this page to reflect the current status of the campaign.

Current target sources:

Z Cam

YZ Cnc

EM Cyg