(T.J. Johnson (Praxis), M. Kerr (NRL), P. S. Ray (NRL), on behalf of the Fermi LAT Collaboration, and M. Chernyakova (DCU))
There are three well-studied Be star binaries where the neutron star (NS) member has a spin period in the 10ms < spin period < 200 ms, namely PSR B1259-63, A0538-66, and PSR J2032+4127. PSRs B1259 and J2032 have spin periods known from rotation-powered pulsations; that of A0538 is known from accretion-powered pulsation. Prior to recognition of the binary nature of PSR J2032, it was common to note commonalities between PSR B1259-63 and A0538-66, no other similar objects being known. This talk will review the idea that these three systems are members of a rare, transitional class. It will use 2017 periastron passage multi-wavelength observations of PSRs B1259 and J2032 to make comparison and contrast with A0538-66, which has remained at reduced activity over the past decade. Comparison will also be made with other populations that overlap in some characteristics with these sources, namely ULX pulsing (NS) sources and accreting pulsars in Be systems. A preliminary schema for unifying these observations and reconciling differences will be described. Useful further observations will be identified. Fermi work at NRL is supported by NASA.