Intermediate mass binary pulsars

2.7 Intermediate mass binary pulsars

The range of white dwarf masses observed is becoming broader. Since this article originally appeared [221 ], the number of “intermediate-mass binary pulsars” [54 ] has grown significantly [58

]. These systems are distinct to the millisecond pulsar–white dwarf binaries in several ways:

The spin period of the radio pulsar is generally longer (9 – 200 ms).
The mass of the white dwarf is larger (typically $≳ 0.5 M ⊙$ ).
The orbit, while still essentially circular, is often significantly more eccentric ( $e ≳ 10 −3$ ).
The binary parameters do not necessarily follow the mass–period or eccentricity–period relationships.

It is not presently clear whether these systems originated from low- or high-mass X-ray binaries. It was suggested by van den Heuvel [383 ] that they have more in common with high-mass systems. Subsequently, Li proposed [213 ] that a thermal-viscous instability in the accretion disk of a low-mass X-ray binary could truncate the accretion phase and produce a more slowly spinning neutron star.