A fraction of very low mass stars and brown dwarfs are known to be radio active , in some cases producing periodic pulses .
Extensive studies of two such objects have also revealed optical periodic variability and the nature of this variability remains unclear .
Here we report on multi-epoch optical photometric monitoring of six radio detected dwarfs , spanning the \sim M8 - L3.5 spectral range , conducted to investigate the ubiquity of periodic optical variability in radio detected ultracool dwarfs .
This survey is the most sensitive ground-based study carried out to date in search of periodic optical variability from late-type dwarfs , where we obtained 250 hours of monitoring , delivering photometric precision as low as \sim 0.15 % .
Five of the six targets exhibit clear periodicity , in all cases likely associated with the rotation period of the dwarf , with a marginal detection found for the sixth .
Our data points to a likely association between radio and optical periodic variability in late-M/early-L dwarfs , although the underlying physical cause of this correlation remains unclear .
In one case , we have multiple epochs of monitoring of the archetype of pulsing radio dwarfs , the M9 TVLM 513-46546 , spanning a period of 5 years , which is sufficiently stable in phase to allow us to establish a period of 1.95958 \pm 0.00005 hours .
This phase stability may be associated with a large-scale stable magnetic field , further strengthening the correlation between radio activity and periodic optical variability .
Finally , we find a tentative spin-orbit alignment of one component of the very low mass binary LP 349-25 .