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

TL;DR

This paper proposes that very faint X-ray transients are wind-fed binary systems with detached M-dwarf donors in the period gap, explaining their faintness and low duty cycle through a new evolutionary scenario.

Contribution

It introduces a novel wind-fed detached binary model for very faint X-ray transients within the period gap, aligning with observed properties.

Findings

The scenario reproduces the faintness of the transients.

It explains their low duty cycle and low mass transfer rates.

Proposes observational tests for the model.

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.