Searching for Black Widow and Redback Pulsar Analogues with the Long Wavelength Array

There exists a well known connection between gamma-ray emission and millisecond pulsars (MSPs) and there is also some evidence for a connection between gamma-ray emission and black widow and redback pulsar systems. These black widow and redback pulsar systems have been shown to have periodic dispersion measure (DM) variations on timescales near that of the binary period. This variation in DM arises from the pulse traveling through material present within the systems. The exact conditions which separate “normal” MSP systems from black widows and redbacks are not well understood. We have observed four binary pulsar systems, two of which show gamma-ray emission, which have known white dwarf companions in order to search for similar periodic DM variations. The expected DM variations are small as white dwarfs contribute little material to the system due to their strong gravity and theoretically weak stellar winds. The low frequencies observed by the Long Wavelength Array (LWA) make us highly sensitive to DM variations. We report changes in DM nearly 3 orders of magnitude smaller than seen in black widow systems, but find no periodic variations.