Origin of magnetars in binary systems

I review several scenarios of magnetar formation in binary systems via spin-up of a progenitor due to interaction with its companion. Mostly, these evolutionary channels lead to formation of isolated magnetars, and indeed, all well-established sources of this class are single objects. However, some binaries can survive, and several candidates to accreting magnetars have been proposed. I discuss this issue, and conclude that new accretion models can explain properties of the proposed candidates without large magnetic field in correspondence with models of magnetic field evolution.