We report on the discovery of large-amplitude flickering from V648 Car ( = SS73-17 ) , a poorly studied object listed amongst the very few hard X-ray emitting symbiotic stars .
We performed milli-magnitude precision optical photometry with the Swope Telescope at the Las Campanas Observatory , Chile , and found that V648 Car shows large U-band variability over time scales of minutes .
To our knowledge , it is amongst the largest flickering of a symbiotic star ever reported .
Our finding supports the hypothesis that symbiotic WDs producing hard X-rays are predominantly powered by accretion , rather than quasi-steady nuclear burning , and have masses close to the Chandrasekhar limit .
No significant periodicity is evident from the flickering light curve .
The ASAS long-term V light curve suggests the presence of a tidally distorted giant accreting via Roche Lobe overflow , and a binary period of \sim 520 days .
On the basis of the outstanding physical properties of V648 Car as hinted by its fast and long-term optical variability , as well as by its nature as hard X-ray emitter , we therefore call for simultaneous follow-up observations in different bands , ideally combined with time-resolved optical spectroscopy .