Are the very faint X-ray transients period gap systems?

Abstract

We discuss a scenario for the very faint X-ray transients as X-ray binaries fed by winds from detached M dwarf donors in binary stars within the 'period gap'-the range of periods where donor stars have become fully convective, and shrunken so that they no longer fill their Roche lobes, but have not yet re-attached due to the systems shrinking through gravitational radiation. This wind-fed detached binary scenario can reproduce the two key properties of the very faint X-ray transients-their faintness, which defines them, and their relatively low duty cycle outbursts which require that they have low mean mass transfer rates. We discuss feasible observational tests of the scenario. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.