Fermi LAT Observations of Two Be-Pulsar Binary Systems at GeV Energies

A small, but growing, number of binary systems comprising a compact object (neutron star or black hole) orbiting a massive Be or O type star are seen to emit phase-varying, non-thermal radiation from radio waves up to TeV gamma rays. The nature of the compact object is only definitively known in two systems, both comprising a young, rotation-powered pulsar and a Be star. The PSR B1259-63 system has an orbital period of 3.4 years and Fermi has observed 3 periastron passages. Enhanced GeV emission appears after periastron, with the most-recent event, in Autumn of 2017, displaying rapid variability on a timescale of minutes. The only observed periastron in the 50-year-period PSR J2032+4127 system occurred in November of 2017. We will describe GeV observations of both periastron passages. Comparisons will be made with a third well-studied Be star binary system, A0538-66, where the neutron star member has a similarly short spin period known from a transient accretion episode, and with ULX accreting pulsars. Fermi work at NRL is supported by NASA.