5 Conclusions

The main results of the present paper are the following:

1.

The spectral analysis of the data shows a main peak at 52 $\pm$ 5 days, in agreement with the orbital period of 51.075 days.

2.

The data folded with the orbital period clusters at the periastron passage.

3.

A detailed monitoring of an activity period around periastron reveals a regular pattern in agreement with the rotational period of the star spots, inferred from optical observations.

On that basis we conclude that a scenario of flares originating in recurrent collisions of giant loops, anchored on the two stars of the system, during the periastron passage, is the most straightforward interpretation.

The fact that a strong flare at 7 mm and a lower one at 2.8 cm occur outside the periastron passages certainly is not enough to rule out the above scenario or to suggest a new one. However, the similarities with other periodicities discussed in Sect. 4 remain very appealing. We conclude that only future observations will definitely support the choice between the two scenarios of an inter-binary collision (depending on the binary nature) or of an intrinsic mechanism originating in the stellar interior (and therefore also common to other stars).

Acknowledgements

We wish to thank Guidetta Torricelli, Ulrich Mebold, Christian Henkel, Franca Drago and Alexander Kraus for their comments and support. Special thanks also go to the staff of the Effelsberg telescope and the VLA. The VLA is operated by the National Radio Astronomy Observatory (NRAO) with Associated Universities Inc. and is funded by the NSF.