  A0535+26 is shown to display quantised IR excess flux states, which are
interpreted as the first observational verification of the resonant truncation
scheme proposed by Okazaki and Negueruela (2001) for BeXRBs. The simultaneity
of X-ray activity with transitions between these states strongly suggests a
broad mechanism for outbursts, in which material lost from the disc during the
reduction of truncation radius is accreted by the NS. Furthermore changes
between states are shown to be governed by a 1500 day period, probably due to
precession of the Be disc, which profoundly dictates the global behaviour of
the system. Such a framework appears to be applicable to BeXRBs in general.

Astrophysics